JP2011129891A - Semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor device having a radio communication function, which can reduce power consumption or can prolong a life. <P>SOLUTION: The semiconductor device can solve a problem by electrically connecting a battery as a power supply source to a specific circuit through a transistor in which a channel formation region is composed of an oxide semiconductor. A hydrogen concentration of the oxide semiconductor is 5×10<SP>19</SP>(atoms/cm<SP>3</SP>) or less. Therefore, a leak current of the transistor can be reduced. As a result, power consumption during stand-by of the semiconductor device can be reduced. In addition, this leads to a prolonged life of the semiconductor device. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a semiconductor device. In particular, the present invention relates to a semiconductor device having a wireless communication function.

  Note that in this specification, a semiconductor device refers to all devices that can function by utilizing semiconductor characteristics, and an electro-optical device, a semiconductor circuit, and an electronic device are all semiconductor devices.

  A semiconductor device having a wireless communication function capable of transmitting and receiving data wirelessly has been put into practical use in various fields. Such a semiconductor device is expected to expand further as a new type of communication information terminal. In a semiconductor device having a wireless communication function in practical use, an antenna and an integrated circuit formed using a semiconductor element are formed over the same substrate. A semiconductor device having a wireless communication function is also referred to as a wireless tag, an RF (Radio Frequency) tag, an RFID (Radio Frequency Identification) tag, an IC (Integrated Circuit) tag, or an ID (Identification) tag.

  The semiconductor device is roughly classified into two types, an active type and a passive type. The former is a semiconductor device that has a battery in the semiconductor device and operates using the battery as a power supply source. The latter does not have a power supply source such as a battery in the semiconductor device, and an external interrogator (reader). , A reader / writer, also referred to as R / W), which operates as a power supply source.

  Since the active wireless tag has a built-in power supply source, the communication distance to the interrogator can be made longer than that of the passive wireless tag. However, since the active wireless tag operates (signal generation) constantly or periodically regardless of the presence or absence of an interrogator that responds, power consumption increases.

  Patent Document 1 discloses a technique for reducing the power consumption of an active wireless tag. In addition to the configuration of the conventional active wireless tag, the active wireless tag (active wireless tag) disclosed in Patent Document 1 generates power using a second antenna that receives a signal from the outside and the signal. The generator includes a generator and a voltage detection circuit to which the output voltage of the generator is input, and the intermittent operation is controlled by the voltage detection circuit. Thereby, power consumption can be reduced.

JP 2006-229558 A

  However, power consumed by a semiconductor device that performs intermittent operation includes not only power consumption during operation but also power consumption during standby (hereinafter also referred to as standby power). Here, standby power refers to power consumption resulting from a small amount of discharge through an element or circuit to which a battery is electrically connected. In particular, in the semiconductor device capable of controlling the intermittent operation disclosed in Patent Document 1, the ratio of standby power to the power consumption increases. Therefore, in order to reduce power consumption in the semiconductor device, it is important to reduce standby power.

  Thus, an object of one embodiment of the present invention is to reduce standby power of a semiconductor device.

  Another object of one embodiment of the present invention is to extend the life of a semiconductor device.

  The above problem can be solved by electrically connecting a battery serving as a power supply source and a specific circuit through a transistor whose channel formation region is formed using an oxide semiconductor. Note that the oxide semiconductor is an intrinsic or substantially intrinsic semiconductor by removing hydrogen which serves as an electron donor (donor).

Specifically, hydrogen contained in the oxide semiconductor is 5 × 10 ¹⁹ (atoms / cm ³ ) or less, preferably 5 × 10 ¹⁸ (atoms / cm ³ ) or less, and more preferably 5 × 10 ¹⁷ (atoms / cm ³ ). cm ³ ) or less. By reducing the hydrogen concentration in this way, the carrier density is less than 1 × 10 ¹⁴ cm ⁻³ , preferably less than 1 × 10 ¹² cm ⁻³ , more preferably less than 1 × 10 ¹¹ cm ⁻³ below the measurement limit. It becomes possible to do.

By using such a highly purified oxide semiconductor for a channel formation region of a transistor, the drain current in the off state of the transistor is 1 × 10 ⁻¹³ [A] or less even when the channel width is 10 mm. It acts to become. In other words, when a highly purified oxide semiconductor is used for a channel formation region of a transistor, leakage current can be significantly reduced.

In other words, according to one embodiment of the present invention, an antenna, a battery, a demodulation circuit that demodulates a signal input from the antenna, a signal input from the demodulation circuit, and a signal processing that operates using a power supply voltage supplied from the battery And a power control circuit controlled by a signal input from the demodulation circuit, the signal processing unit includes a transistor whose switching is controlled by a signal input from the power control circuit, and a battery via the transistor And a functional circuit electrically connected to the anode or the cathode of the transistor, and a channel formation region of the transistor is formed of an oxide semiconductor having a hydrogen concentration of 5 × 10 ¹⁹ (atoms / cm ³ ) or less It is.

The demodulation circuit included in the above configuration can be replaced with a timer. That is, it is controlled by an antenna, a battery, a timer that periodically outputs a signal, a signal input from the timer and a power supply voltage supplied from the battery, and a signal input from the timer. A power control circuit, a signal processing unit having a transistor whose switching is controlled by a signal input from the power control circuit, and a function electrically connected to the anode or cathode of the battery via the transistor A semiconductor device including a circuit in which a channel formation region of a transistor is formed using an oxide semiconductor with a hydrogen concentration of 5 × 10 ¹⁹ (atoms / cm ³ ) or less is also an embodiment of the present invention.

  In addition to the above configuration, the battery having the above configuration is a secondary battery, and in addition to the above configuration, a rectifier circuit that rectifies a signal input from the antenna, and charging that charges the secondary battery using the signal input from the rectifier circuit A semiconductor device including a circuit and a stabilized power supply circuit that generates a power supply voltage using a secondary battery is also one embodiment of the present invention.

  Examples of the functional circuit include a logic gate. The logic gate can be composed of a complementary metal oxide semiconductor (CMOS) or can be composed of only an N-type transistor (NMOS).

A semiconductor device of one embodiment of the present invention includes a functional circuit, a battery, and a transistor that controls electrical connection between the functional circuit and the battery. The channel formation region of the transistor is formed using an oxide semiconductor with a reduced hydrogen concentration. Specifically, the hydrogen concentration of the oxide semiconductor is 5 × 10 ¹⁹ (atoms / cm ³ ) or less. Therefore, by turning off the transistor in the standby state, discharge through the transistor can be suppressed. As a result, standby power of the semiconductor device can be reduced. In addition, the life of the semiconductor device can be extended by reducing the discharge of the battery in the standby state.

FIG. 3 illustrates a configuration example of a semiconductor device described in Embodiment 1; FIG. 6 illustrates a configuration example of a semiconductor device described in Embodiment 2; FIG. 6 illustrates a configuration example of a semiconductor device described in Embodiment 3; FIG. 6 illustrates a configuration example of a semiconductor device described in Embodiment 4; FIGS. 9A to 9C are diagrams illustrating a configuration example of a logic gate included in a semiconductor device described in Embodiment 4; FIGS. FIGS. 9A to 9C are diagrams illustrating a configuration example of a logic gate included in a semiconductor device described in Embodiment 4; FIGS. 9 is a cross-sectional view illustrating a structure example of a P-type transistor and an N-type transistor described in Embodiment 5. FIG. FIGS. 9A to 9H are cross-sectional views illustrating an example of a manufacturing process of a P-type transistor described in Embodiment 5. FIGS. FIGS. 6A to 6G are cross-sectional views illustrating an example of a manufacturing process of an N-type transistor described in Embodiment 5. FIGS. FIGS. 9A to 9D are cross-sectional views illustrating an example of a manufacturing process of an N-type transistor described in Embodiment 5. FIGS. 9 is a cross-sectional view illustrating a structure example of a P-type transistor and an N-type transistor described in Embodiment 5. FIG. FIGS. 6A and 6B are cross-sectional views illustrating structural examples of a P-type transistor and an N-type transistor described in Embodiment 5. FIGS. FIGS. 7A and 7B are cross-sectional views illustrating structural examples of a P-type transistor and an N-type transistor described in Embodiment 5. FIGS. FIGS. 6A and 6B are cross-sectional views illustrating structural examples of a P-type transistor and an N-type transistor described in Embodiment 5. FIGS. FIGS. 9A and 9B are cross-sectional views illustrating a structure example of a transistor described in Embodiment 6; FIGS. FIGS. 9A to 9E are cross-sectional views illustrating an example of a manufacturing process of a transistor described in Embodiment 6; FIGS. FIGS. 9A to 9E are cross-sectional views illustrating an example of a manufacturing process of a transistor described in Embodiment 7. FIGS. FIGS. 9A to 9D are cross-sectional views illustrating an example of a manufacturing process of a transistor described in Embodiment 8. FIGS. FIG. 10 illustrates a usage example of a semiconductor device described in Embodiment 9;

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it is easily understood by those skilled in the art that modes and details can be variously changed without departing from the spirit and scope of the present invention. Therefore, the present invention should not be construed as being limited to the description of the embodiments below.

  Note that since the source terminal and the drain terminal of a transistor are changed depending on the structure, operating conditions, and the like of the transistor, it is difficult to specify which is a source terminal or a drain terminal. Therefore, in this document, one of the source terminal and the drain terminal is referred to as a first terminal, and the other of the source terminal and the drain terminal is referred to as a second terminal.

  In addition, the size, the layer thickness, or the region of each structure illustrated in the drawings and the like in the embodiments is exaggerated for simplicity in some cases. Therefore, it is not necessarily limited to the scale. In addition, ordinal numbers such as “first”, “second”, and “third” used in the present specification are given to avoid confusion between components, and are not limited numerically. Is added.

(Embodiment 1)
In this embodiment, an example of a semiconductor device is described. Specifically, an example of a semiconductor device having a wireless communication function using a battery as a power supply source will be described with reference to FIG.

  A semiconductor device illustrated in FIG. 1 includes an antenna 10 capable of transmitting and receiving a radio signal, a battery 11 serving as a supply source of a power supply voltage (VDD), a demodulation circuit 12 that demodulates a signal input from the antenna 10, and a demodulation circuit. 12, and a signal processing unit 13 that operates using a power supply voltage (VDD) supplied from the battery 11 and a signal input from the battery 11, a signal input from the demodulation circuit 12, and a signal input from the signal processing unit 13. Power control circuit 14. In the present embodiment, the operation refers to signal generation performed in the signal processing unit 13 or a part of the signal processing unit 13.

  Further, the signal processing unit 13 includes a transistor 15 whose switching is controlled by a signal input from the power control circuit 14. Specifically, the switching of the transistor 15 from the off state to the on state is controlled by a signal input from the demodulation circuit 12 to the power control circuit 14, and the transistor 15 is controlled by a signal input from the signal processing unit 13 to the power control circuit 14. Switching from the on state to the off state is controlled.

  The signal processing unit 13 includes a functional circuit (not shown) that operates using the signal input from the demodulation circuit 12 and the power supply voltage (VDD). Note that the transistor 15 is provided between the functional circuit and the anode or cathode of the battery 11. That is, the functional circuit is electrically connected to the anode or cathode of the battery 11 through the transistor 15. In addition, the functional circuit can operate during a period in which the transistor 15 is on.

The channel formation region of the transistor 15 has a hydrogen concentration of 5 × 10 ¹⁹ (atoms / cm ³ ) or less, preferably 5 × 10 ¹⁸ (atoms / cm ³ ) or less, and more preferably 5 × 10 ¹⁷ (atoms / cm ³ ). ³ ) It is comprised by the following oxide semiconductors. That is, the transistor 15 is a transistor in which a highly purified oxide semiconductor in which hydrogen serving as a carrier donor is reduced to a very low concentration is applied to a channel formation region. Note that the hydrogen concentration in the oxide semiconductor layer was measured by secondary ion mass spectrometry (SIMS).

  Thereby, the leakage current of the transistor 15 can be significantly reduced. In addition, in the semiconductor device of the present embodiment, the transistor 15 is kept off in the standby state. Therefore, discharge of the battery 11 in the standby state can be suppressed. That is, the standby power of the semiconductor device can be reduced. In addition, the life of the semiconductor device can be extended by suppressing the discharge of the battery 11 in the standby state.

<Modification>
Note that the semiconductor device described above is an example of the semiconductor device of this embodiment, and a semiconductor device having a different point from the semiconductor device described above is also included in this embodiment.

  For example, in the semiconductor device described above, the transistor 15 is described as being provided between the functional circuit and the anode or the cathode of the battery 11; however, the semiconductor device of this embodiment is not limited to this structure. In the semiconductor device of this embodiment, the transistor 15 may be a component of a functional circuit. Further, the transistor 15 is not necessarily connected directly to the battery 11. It may be provided in the functional circuit while maintaining the function by changing the order of the circuit or the transistor connected in series.

  In the above-described semiconductor device, the switching from the on state to the off state of the transistor 15 has been described with respect to the configuration controlled by the output signal of the signal processing unit 13, but the semiconductor device of the present embodiment has the above configuration. It is not limited. In the semiconductor device of the present embodiment, the switching from the on state to the off state of the transistor 15 may be controlled by a signal input from the demodulation circuit 12. Alternatively, the transistor 15 may be switched from the on state to the off state after a specific time has elapsed since the transistor 15 was switched from the off state to the on state.

  Note that the content of this embodiment or part of the content can be freely combined with the content of another embodiment or part of the content.

(Embodiment 2)
In this embodiment, an example of a semiconductor device is described. Specifically, an example of a semiconductor device having a wireless communication function using a battery as a power supply source will be described with reference to FIG.

  The semiconductor device illustrated in FIG. 2 controls the intermittent operation of the semiconductor device by periodically outputting a signal, and an antenna 20 capable of transmitting and receiving a radio signal, a battery 21 serving as a power supply voltage (VDD) supply source, and the like. Timer 22, a signal input from timer 22, a signal processing unit 23 that operates using a power supply voltage (VDD) supplied from battery 21, and a signal input from timer 22 and a signal processing unit 23. And a power control circuit 24 controlled by a signal. In the present embodiment, the operation refers to signal generation performed in the signal processing unit 23 or a part of the signal processing unit 23.

  Further, the signal processing unit 23 includes a transistor 25 whose switching is controlled by a signal input from the power control circuit 24. Specifically, the transistor 25 is controlled to be switched from the off state to the on state by a signal input from the timer 22 to the power control circuit 24 and is turned on by a signal input from the signal processing unit 23 to the power control circuit 24. Switching from state to off state is controlled.

  Further, the signal processing unit 23 has a functional circuit (not shown) that operates using the output signal of the timer 22 and the power supply voltage (VDD). Note that the transistor 25 is provided between the functional circuit and the anode or the cathode of the battery 21. That is, the functional circuit is electrically connected to the anode or cathode of the battery 21 via the transistor 25. In addition, the functional circuit can operate during a period in which the transistor 25 is on.

The channel formation region of the transistor 25 has a hydrogen concentration of 5 × 10 ¹⁹ (atoms / cm ³ ) or less, preferably 5 × 10 ¹⁸ (atoms / cm ³ ) or less, and more preferably 5 × 10 ¹⁷ (atoms / cm ³ ). ³ ) It is comprised by the following oxide semiconductors. That is, the transistor 25 is a transistor in which a highly purified oxide semiconductor in which hydrogen serving as a carrier donor is reduced to a very low concentration is applied to a channel formation region. Note that the hydrogen concentration in the oxide semiconductor layer was measured by secondary ion mass spectrometry (SIMS).

  Thereby, the leakage current of the transistor 25 can be significantly reduced. In addition, in the semiconductor device of this embodiment, the transistor 25 is kept off in the standby state. Therefore, discharge of the battery 21 in the standby state can be suppressed. That is, the standby power of the semiconductor device can be reduced. In addition, the life of the semiconductor device can be extended by suppressing the discharge of the battery 21 in the standby state.

<Modification>
Note that the semiconductor device described above is an example of the semiconductor device of this embodiment, and a semiconductor device having a different point from the semiconductor device described above is also included in this embodiment.

  For example, in the above-described semiconductor device, the configuration in which the output signal of the timer 22 is input to the signal processing unit 23 and the power control circuit 24 is described; however, the semiconductor device of the present embodiment is not limited to this configuration. In the semiconductor device of the present embodiment, the output signal of the timer 22 may be input only to the power control circuit. Further, the output signal of the signal processing unit 23 may be input to the timer 22. For example, when the signal processing unit 23 outputs a reset signal of the timer 22 and inputs the reset signal to the timer 22, the next operation timing can be controlled.

  Note that the content of this embodiment or part of the content can be freely combined with the content of another embodiment or part of the content.

(Embodiment 3)
In this embodiment, an example of a semiconductor device is described. Specifically, an example of a semiconductor device having a wireless communication function using a secondary battery as a power supply source will be described with reference to FIGS.

  The semiconductor device illustrated in FIG. 3 includes an antenna 30 capable of transmitting and receiving radio signals, a secondary battery 31 serving as a power supply source, a rectifier circuit 32 that rectifies a signal input from the antenna 30, and an input from the rectifier circuit 32. A charging circuit 33 that charges the secondary battery 31 using the generated signal, a stabilized power circuit 34 that generates the power supply voltage (VDD) used in the semiconductor device using the secondary battery 31, and the antenna 30. A demodulating circuit 35 that demodulates a signal input from the signal, a signal processing unit 36 that operates using the signal input from the demodulating circuit 35 and the power supply voltage (VDD) supplied from the stabilized power circuit 34, and a demodulating circuit 35 And a power control circuit 37 controlled by a signal input from the signal processing unit 36. In the present embodiment, the operation refers to signal generation performed in the signal processing unit 36 or a part of the signal processing unit 36.

  Further, the signal processing unit 36 includes a transistor 38 whose switching is controlled by a signal input from the power control circuit 37. Specifically, the switching of the transistor 38 from the off state to the on state is controlled by a signal input from the demodulation circuit 35 to the power control circuit 37, and the transistor 38 is controlled by a signal input from the signal processing unit 36 to the power control circuit 37. Switching from the on state to the off state is controlled.

  The signal processing unit 36 includes a functional circuit (not shown) that operates using the signal input from the demodulation circuit 35 and the power supply voltage (VDD). Note that the transistor 38 is provided between the functional circuit and the stabilized power supply circuit 34. That is, the functional circuit is electrically connected to the anode or cathode of the secondary battery 31 via the transistor 38 and the stabilized power circuit 34. In addition, the functional circuit can operate during a period in which the transistor 38 is on.

The channel formation region of the transistor 38 has a hydrogen concentration of 5 × 10 ¹⁹ (atoms / cm ³ ) or less, preferably 5 × 10 ¹⁸ (atoms / cm ³ ) or less, and more preferably 5 × 10 ¹⁷ (atoms / cm ³ ). ³ ) It is comprised by the following oxide semiconductors. That is, the transistor 38 is a transistor in which a highly purified oxide semiconductor in which hydrogen serving as a carrier donor is reduced to an extremely low concentration is applied to a channel formation region. Note that the hydrogen concentration in the oxide semiconductor layer was measured by secondary ion mass spectrometry (SIMS).

  Thereby, the leakage current of the transistor 38 can be significantly reduced. In addition, in the semiconductor device of the present embodiment, the transistor 38 is kept off in the standby state. Therefore, discharge of the secondary battery 31 in the standby state can be suppressed. That is, the standby power of the semiconductor device can be reduced. In addition, the life of the semiconductor device can be extended by suppressing the discharge of the secondary battery 31 in the standby state.

  Further, the semiconductor device illustrated in FIG. 3 can charge the secondary battery 31 by a signal input from the antenna 30. Note that the semiconductor device can be charged in parallel during operation, and can be charged using a signal input from the antenna 30 in a standby state.

  In the semiconductor device, if the same level of power as standby power is always charged, the battery will not run out. Further, the semiconductor device includes the transistor 38 as described above, whereby standby power can be reduced. Thereby, the chargeable distance of the semiconductor device can be improved. The semiconductor device of this embodiment having such characteristics is particularly effective in places where access is difficult (in the body, radioactivity, space where powerful drugs are present, or a vacuum space).

<Modification>
Note that the semiconductor device described above is an example of the semiconductor device of this embodiment, and a semiconductor device having a different point from the semiconductor device described above is also included in this embodiment.

  For example, in the above-described semiconductor device, the structure in which the antenna 30 is provided and the antenna 30 is used to transmit and receive a radio signal and charge the secondary battery 31 is described. It is not limited to the configuration. The semiconductor device of this embodiment may have a configuration in which an antenna for transmitting and receiving radio signals and an antenna for charging the secondary battery 31 are separately provided.

  Note that the content of this embodiment or part of the content can be freely combined with the content of another embodiment or part of the content.

(Embodiment 4)
In this embodiment, an example of a semiconductor device is described. Specifically, an example of a semiconductor device having a wireless communication function using a secondary battery as a power supply source will be described with reference to FIGS.

  The semiconductor device illustrated in FIG. 4 includes an antenna 40 capable of transmitting and receiving radio signals, a secondary battery 41 serving as a power supply source, a rectifier circuit 42 that rectifies a signal input from the antenna 40, and an output of the rectifier circuit 42. A charging circuit 43 that charges the secondary battery 41 using a signal, a stabilized power circuit 44 that generates a power supply voltage (VDD) used in the semiconductor device using the secondary battery 41, and an input from the antenna 40 A demodulating circuit 45 that demodulates the received signal, a signal processing unit 46 that operates using the signal input from the demodulating circuit 45 and the power supply voltage (VDD) supplied from the stabilized power circuit 44, and an input from the demodulating circuit 45 And a power control circuit 47 controlled by a signal input from the signal processing unit 46. In the present embodiment, the operation refers to signal generation performed in the signal processing unit 46 or a part of the signal processing unit 46.

  Further, the signal processing unit 46 includes a logic circuit 48 that performs processing using a signal input from the demodulation circuit 45, a clock generation circuit 49 that generates a clock signal (CK) used in the semiconductor device, a specific circuit It has a sensor 50 that converts external information into a signal, a memory circuit 51 that stores information, and a modulation circuit 52 that applies load modulation to the antenna 40. Note that a standby signal (Stdby) output from the power control circuit 47 is input to each of the logic circuit 48, the clock generation circuit 49, the sensor 50, the memory circuit 51, and the modulation circuit 52.

  Various circuits included in the semiconductor device of this embodiment include transistors. Here, a specific circuit configuration example of a logic gate (an inverter (NOT gate), a NOR gate, and a NAND gate) included in the logic circuit 48 will be described with reference to FIG.

  FIG. 5A shows a specific circuit configuration example of the inverter. The inverter illustrated in FIG. 5A includes a P-type transistor 80, an N-type transistor 81, and an N-type transistor 82.

  The P-type transistor 80 is electrically connected to a wiring whose first terminal supplies a power supply voltage (VDD).

  N-type transistor 81 has a first terminal electrically connected to a second terminal of P-type transistor 80.

  The N-type transistor 82 has a gate terminal electrically connected to a wiring for supplying a standby signal (Stdby), a first terminal electrically connected to a second terminal of the N-type transistor 81, and a second terminal grounded. The

  5A, an input signal is input to the gate terminals of the P-type transistor 80 and the N-type transistor 81, and the second terminal of the P-type transistor 80 and the first terminal of the N-type transistor 81 are electrically connected. The potential of the node to be connected is output as the output signal of the inverter.

  FIG. 5B shows a specific circuit configuration example of the NOR gate. The NOR gate illustrated in FIG. 5B includes a P-type transistor 83, a P-type transistor 84, an N-type transistor 85, an N-type transistor 86, and an N-type transistor 87.

  The P-type transistor 83 is electrically connected to a wiring whose first terminal supplies a power supply voltage (VDD).

  P-type transistor 84 has a first terminal electrically connected to a second terminal of P-type transistor 83.

  N-type transistor 85 has a first terminal electrically connected to a second terminal of P-type transistor 84.

  The N-type transistor 86 has a first terminal electrically connected to the second terminal of the P-type transistor 84 and the first terminal of the N-type transistor 85.

  The N-type transistor 87 has a gate terminal electrically connected to a wiring for supplying a standby signal (Stdby), and a first terminal electrically connected to the second terminal of the N-type transistor 85 and the second terminal of the N-type transistor 86. Connected and the second terminal is grounded.

  5B, the first input signal is applied to the gate terminals of the P-type transistor 83 and the N-type transistor 86, and the second input is applied to the gate terminals of the P-type transistor 84 and the N-type transistor 85. A signal is input, and a potential of a node electrically connected to the second terminal of the P-type transistor 84, the first terminal of the N-type transistor 85, and the first terminal of the N-type transistor 86 is output as an output signal of the NOR gate. The

  FIG. 5C shows a specific circuit configuration example of the NAND gate. The NAND gate illustrated in FIG. 5C includes a P-type transistor 88, a P-type transistor 89, an N-type transistor 90, an N-type transistor 91, and an N-type transistor 92.

  The P-type transistor 88 is electrically connected to a wiring whose first terminal supplies a power supply voltage (VDD).

  The P-type transistor 89 is electrically connected to a wiring whose first terminal supplies a power supply voltage (VDD).

  N-type transistor 90 has a first terminal electrically connected to a second terminal of P-type transistor 88 and a second terminal of P-type transistor 89.

  N-type transistor 91 has a first terminal electrically connected to a second terminal of N-type transistor 90.

  The N-type transistor 92 has a gate terminal electrically connected to a wiring for supplying a standby signal (Stdby), a first terminal electrically connected to a second terminal of the N-type transistor 91, and a second terminal grounded. The

  5C, the first input signal is applied to the gate terminals of the P-type transistor 88 and the N-type transistor 90, and the second input is applied to the gate terminals of the P-type transistor 89 and the N-type transistor 91. A signal is input, and a potential of a node electrically connected to the second terminal of the P-type transistor 88, the second terminal of the P-type transistor 89, and the first terminal of the N-type transistor 90 is output as an output signal of the NAND gate. The

The above-described logic gate includes a transistor (an N-type transistor 82, an N-type transistor 87, or an N-type transistor 92) that controls electrical connection with a wiring that supplies a ground potential. In the logic gate, the channel formation region of the transistor has a hydrogen concentration of 5 × 10 ¹⁹ (atoms / cm ³ ) or less, preferably 5 × 10 ¹⁸ (atoms / cm ³ ) or less, more preferably 5 × 10 9. ¹⁷ (atoms / cm ³ ) or less of an oxide semiconductor. Thereby, the leakage current of the transistor can be significantly reduced. Therefore, it becomes possible to reduce the through current flowing through the logic gate. As a result, standby power of the semiconductor device can be reduced.

  Note that although a structure in which each logic gate includes a transistor that controls input of the ground potential is described here, a structure in which input of the ground potential to a plurality of logic gates is controlled by one transistor may be employed.

  In the above description, an example in which a logic gate is configured by a complementary metal oxide semiconductor (CMOS) has been described. However, the semiconductor device of this embodiment can also be configured by only an N-type transistor. FIG. 6 shows a logic gate composed of only N-type transistors. 6A is an inverter, FIG. 6B is a NOR gate, and FIG. 6C is a NAND gate. In short, the logic gate shown in FIG. 6 has a structure in which the P-type transistor included in the logic gate shown in FIG. 5 is replaced with a diode-connected N-type transistor.

As described above, the logic gate illustrated in FIGS. 6A to 6C is a transistor that controls electrical connection with a wiring that supplies a ground potential, and the hydrogen concentration in the channel formation region is 5 × 10 ¹⁹ ( A transistor including an oxide semiconductor of atoms / cm ³ ) or less, preferably 5 × 10 ¹⁸ (atoms / cm ³ ) or less, more preferably 5 × 10 ¹⁷ (atoms / cm ³ ) or less is used. Thereby, the leakage current of the transistor can be significantly reduced. Therefore, it becomes possible to reduce the through current flowing through the logic gate. As a result, standby power of the semiconductor device can be reduced.

  The clock generation circuit 49, the sensor 50, the memory circuit 51, and the modulation circuit 52 also supply wiring for supplying the circuit and the ground potential or the circuit and the power supply potential (VDD) based on the conventional circuit configuration. A transistor whose switching is controlled by the power control circuit 47 may be provided between the wirings to be connected. Further, a transistor controlled by the power control circuit 47 may be provided in units of blocks constituting the conventional circuit configuration, or a transistor controlled by the power control circuit 47 may be provided in units of functional circuits.

  Note that the content of this embodiment or part of the content can be freely combined with the content of another embodiment or part of the content.

(Embodiment 5)
In this embodiment, an example of a transistor included in the semiconductor device described in any of Embodiments 1 to 4 will be described. Specifically, an example in which a transistor formed using a substrate including a semiconductor material is used as a P-type transistor included in the semiconductor device, and a transistor formed using an oxide semiconductor is applied as an N-type transistor. Indicates.

<Configuration example>
FIG. 7 shows a P-type transistor and an N-type transistor included in the semiconductor device of this embodiment.

  7 includes a channel formation region 116 provided in a substrate 100 containing a semiconductor material, a pair of impurity regions 114a and 114b provided so as to sandwich the channel formation region 116, and a pair of high-concentration impurities. Regions 120a and 120b (also collectively referred to as impurity regions), a gate insulating layer 108a provided over the channel formation region 116, a gate electrode layer 110a provided over the gate insulating layer 108a, and an impurity region 114a A source electrode layer 130a electrically connected to the impurity region 114b and a drain electrode layer 130b electrically connected to the impurity region 114b.

  Note that a sidewall insulating layer 118 is provided on a side surface of the gate electrode layer 110a. In addition, the substrate 100 containing a semiconductor material has a pair of high-concentration impurity regions 120a and 120b in a region that does not overlap with the sidewall insulating layer 118, and a pair of metal compounds over the pair of high-concentration impurity regions 120a and 120b. Regions 124a and 124b exist. Further, an element isolation insulating layer 106 is provided on the substrate 100 so as to surround the P-type transistor 160, and an interlayer insulating layer 126 and an interlayer insulating layer 128 are provided so as to cover the P-type transistor 160. The source electrode layer 130a and the drain electrode layer 130b are electrically connected to one of the pair of metal compound regions 124a and 124b through openings formed in the interlayer insulating layer 126 and the interlayer insulating layer 128. That is, the source electrode layer 130a is electrically connected to the high concentration impurity region 120a and the impurity region 114a through the metal compound region 124a, and the drain electrode layer 130b is electrically connected to the high concentration impurity region 120b and the metal compound region 124b. The impurity region 114b is electrically connected.

  In addition, an N-type transistor 164 described later includes an insulating layer 108b made of the same material as the gate insulating layer 108a, an electrode layer 110b made of the same material as the gate electrode layer 110a, and a source electrode layer 130a and a drain electrode layer 130b. An electrode layer 130c made of the same material is provided.

  The N-type transistor 164 illustrated in FIG. 7 includes a gate electrode layer 136d provided over the interlayer insulating layer 128, a gate insulating layer 138 provided over the gate electrode layer 136d, and an oxide provided over the gate insulating layer 138. A physical semiconductor layer 140; a source electrode layer 142a provided over the oxide semiconductor layer 140 and electrically connected to the oxide semiconductor layer 140; and a drain electrode layer 142b.

  Here, the gate electrode layer 136 d is provided so as to be embedded in the insulating layer 132 formed over the interlayer insulating layer 128. Similarly to the gate electrode layer 136d, an electrode layer 136a in contact with the source electrode layer 130a and an electrode layer 136b in contact with the drain electrode layer 130b of the P-type transistor 160 are formed. In addition, an electrode layer 136c in contact with the electrode layer 130c is formed.

  A protective insulating layer 144 is provided over the N-type transistor 164 so as to be in contact with part of the oxide semiconductor layer 140, and an interlayer insulating layer 146 is provided over the protective insulating layer 144. . Here, the protective insulating layer 144 and the interlayer insulating layer 146 are provided with openings reaching the source electrode layer 142a and the drain electrode layer 142b. Through the openings, the electrode layer 150d in contact with the source electrode layer 142a, the drain electrode An electrode layer 150e in contact with the layer 142b is formed. Similarly to the electrode layer 150d and the electrode layer 150e, the electrode layer 150a in contact with the electrode layer 136a and the electrode layer in contact with the electrode layer 136b through the openings provided in the gate insulating layer 138, the protective insulating layer 144, and the interlayer insulating layer 146. 150b and an electrode layer 150c in contact with the electrode layer 136c are formed.

Here, the oxide semiconductor layer 140 is highly purified by sufficiently removing impurities such as hydrogen. Specifically, the hydrogen concentration of the oxide semiconductor layer 140 is 5 × 10 ¹⁹ (atoms / cm ³ ) or less. Note that the hydrogen concentration of the oxide semiconductor layer 140 is preferably 5 × 10 ¹⁸ (atoms / cm ³ ) or less, and more preferably 5 × 10 ¹⁷ (atoms / cm ³ ) or less. By using the highly purified oxide semiconductor layer 140 in which the hydrogen concentration is sufficiently reduced, the n-type transistor 164 with extremely excellent off-state current characteristics can be obtained. In this manner, by using the oxide semiconductor layer 140 which is highly purified by sufficiently reducing the hydrogen concentration, leakage current of the N-type transistor 164 can be reduced. Note that the hydrogen concentration in the oxide semiconductor layer 140 is measured by secondary ion mass spectrometry (SIMS).

  An insulating layer 152 is provided over the interlayer insulating layer 146, and an electrode layer 154a, an electrode layer 154b, an electrode layer 154c, and an electrode layer 154d are provided so as to be embedded in the insulating layer 152. Note that the electrode layer 154a is in contact with the electrode layer 150a, the electrode layer 154b is in contact with the electrode layer 150b, the electrode layer 154c is in contact with the electrode layer 150c and the electrode layer 150d, and the electrode layer 154d is in contact with the electrode layer 150e. Touching.

  The source electrode layer 130a included in the P-type transistor 160 described in this embodiment is electrically connected to the electrode layer 136a, the electrode layer 150a, and the electrode layer 154a provided in the upper layer region. Therefore, the source electrode layer 130a of the P-type transistor 160 can be electrically connected to any of the electrode layers included in the N-type transistor 164 provided in the upper layer region by appropriately forming these conductive layers. is there. Similarly, the drain electrode layer 130b included in the P-type transistor can be electrically connected to any of the electrode layers included in the N-type transistor 164 provided in the upper layer region. Although not illustrated in FIG. 7, the gate electrode layer 110 a included in the P-type transistor 160 is electrically connected to one of the electrode layers included in the N-type transistor 164 through the electrode layer provided in the upper layer region. It can also be configured to connect.

  Similarly, the source electrode layer 142a included in the N-type transistor 164 described in this embodiment is electrically connected to the electrode layer 130c and the electrode layer 110b provided in the lower layer region. Therefore, the source electrode layer 130a of the N-type transistor 164 is formed by appropriately forming these conductive layers, whereby the gate electrode layer 142a, the source electrode layer 130a, or the drain electrode layer 130b of the P-type transistor 160 provided in the lower layer region. Can be electrically connected. Although not illustrated in FIG. 7, the gate electrode layer 136 d or the drain electrode layer 142 b included in the N-type transistor 164 is connected to the electrode layer included in the P-type transistor 160 via the electrode layer provided in the lower layer region. It can also be configured to be electrically connected to either.

  Various circuits can be formed by appropriately providing the P-type transistor 160 and the N-type transistor 164 described above. Note that all the N-type transistors 164 included in the circuit need not be transistors formed using an oxide semiconductor, and can be changed as appropriate depending on characteristics required for each transistor. For example, as an N-type transistor included in a logic gate included in a semiconductor device, a transistor formed using a substrate containing a semiconductor material is used, and N for controlling electrical connection between the logic gate and a cathode of a battery As the type transistor, a transistor formed using an oxide semiconductor can be used.

<Example of manufacturing process>
Next, an example of a method for manufacturing the P-type transistor 160 and the N-type transistor 164 will be described. Hereinafter, a method for manufacturing the P-type transistor 160 will be described with reference to FIGS. 8A and 8B, and thereafter, a method for manufacturing the N-type transistor 164 will be described with reference to FIGS.

  First, the substrate 100 including a semiconductor material is prepared (see FIG. 8A). As the substrate 100 including a semiconductor material, a single crystal semiconductor substrate such as silicon or silicon carbide, a polycrystalline semiconductor substrate, a compound semiconductor substrate such as silicon germanium, an SOI substrate, or the like can be used. Here, an example in which a single crystal silicon substrate is used as the substrate 100 including a semiconductor material is described. In general, an “SOI substrate” refers to a substrate having a structure in which a silicon semiconductor layer is provided on an insulating surface. In this specification and the like, a semiconductor layer made of a material other than silicon is provided on an insulating surface. It is used as a concept including the substrate of the configuration. That is, the semiconductor layer included in the “SOI substrate” is not limited to the silicon semiconductor layer. The SOI substrate includes a structure in which a semiconductor layer is provided over an insulating substrate such as a glass substrate with an insulating layer interposed therebetween.

  A protective layer 102 serving as a mask for forming an element isolation insulating layer is formed over the substrate 100 (see FIG. 8A). As the protective layer 102, for example, an insulating layer made of silicon oxide, silicon nitride, silicon nitride oxide, or the like can be used. Note that an impurity element imparting n-type conductivity or an impurity element imparting p-type conductivity may be added to the substrate 100 before and after this step in order to control the threshold voltage of the semiconductor device. Good. When the semiconductor is silicon, phosphorus, arsenic, or the like can be used as an impurity imparting n-type conductivity, for example. As the impurity imparting p-type conductivity, for example, boron, aluminum, gallium, or the like can be used.

  Next, etching is performed using the protective layer 102 as a mask to remove part of the substrate 100 in a region not covered with the protective layer 102 (exposed region). Thus, the isolated semiconductor region 104 is formed (see FIG. 8B). As the etching, dry etching is preferably used, but wet etching may be used. An etching gas and an etchant can be appropriately selected according to the material to be etched.

  Next, an insulating layer is formed so as to cover the semiconductor region 104, and the insulating layer in the region overlapping with the semiconductor region 104 is selectively removed, so that the element isolation insulating layer 106 is formed (see FIG. 8B). ). The insulating layer is formed using silicon oxide, silicon nitride, silicon nitride oxide, or the like. As a method for removing the insulating layer, there are a polishing process such as CMP (Chemical Mechanical Polishing) and an etching process, and any of them may be used. Note that after the semiconductor region 104 is formed or after the element isolation insulating layer 106 is formed, the protective layer 102 is removed.

  Next, an insulating layer is formed over the semiconductor region 104, and a layer containing a conductive material is formed over the insulating layer.

  The insulating layer will be a gate insulating layer later, and is a single layer of a film containing silicon oxide, silicon nitride oxide, silicon nitride, hafnium oxide, aluminum oxide, tantalum oxide, or the like obtained by using a CVD method or a sputtering method. A structure or a stacked structure is preferable. In addition, the insulating layer may be formed by oxidizing and nitriding the surface of the semiconductor region 104 by high-density plasma treatment or thermal oxidation treatment. The high density plasma treatment can be performed using, for example, a mixed gas of a rare gas such as He, Ar, Kr, or Xe and oxygen, nitrogen oxide, ammonia, nitrogen, hydrogen, or the like. Further, the thickness of the insulating layer is not particularly limited, but may be, for example, 1 nm or more and 100 nm or less.

  The layer including a conductive material can be formed using a metal material such as aluminum, copper, titanium, tantalum, or tungsten. Alternatively, the layer including a conductive material may be formed using a semiconductor material such as polycrystalline silicon including a conductive material. There is no particular limitation on the formation method, and various film formation methods such as an evaporation method, a CVD method, a sputtering method, and a spin coating method can be used. Note that in this embodiment, an example of the case where the layer including a conductive material is formed using a metal material is described.

  After that, the insulating layer and the layer containing a conductive material are selectively etched, so that the gate insulating layer 108a and the gate electrode layer 110a are formed (see FIG. 8C).

  Next, an insulating layer 112 is formed to cover the gate electrode layer 110a (see FIG. 8C). Then, boron (B), aluminum (Al), or the like is added to the semiconductor region 104 to form a pair of impurity regions 114a and 114b having a shallow junction depth (see FIG. 8C). Here, boron or aluminum is added to form a P-type transistor. However, when an N-type transistor is formed, an impurity element such as phosphorus (P) or arsenic (As) may be added. . Note that the channel formation region 116 is formed under the gate insulating layer 108a of the semiconductor region 104 by the formation of the pair of impurity regions 114a and 114b (see FIG. 8C). Here, the concentration of the impurity to be added can be set as appropriate. However, when the semiconductor element is highly miniaturized, it is desirable to increase the concentration. Here, the step of forming the pair of impurity regions 114a and 114b after the formation of the insulating layer 112 is employed; however, the step of forming the insulating layer 112 after the formation of the pair of impurity regions 114a and 114b is also employed. good.

  Next, a sidewall insulating layer 118 is formed (see FIG. 8D). The sidewall insulating layer 118 can be formed in a self-aligned manner by forming an insulating layer so as to cover the insulating layer 112 and then applying highly anisotropic etching treatment to the insulating layer. At this time, the insulating layer 112 is preferably partially etched to expose the upper surface of the gate electrode layer 110a and the upper surfaces of the pair of impurity regions 114a and 114b.

  Next, an insulating layer is formed so as to cover the gate electrode layer 110a, the pair of impurity regions 114a and 114b, the sidewall insulating layer 118, and the like. Then, boron (B), aluminum (Al), or the like is added to part of the pair of impurity regions 114a and 114b to form a pair of high-concentration impurity regions 120a and 120b (see FIG. 8E). . Again, when an N-type transistor is formed, an impurity element such as phosphorus (P) or arsenic (As) may be added. After that, the insulating layer is removed, and a metal layer 122 is formed so as to cover the gate electrode layer 110a, the sidewall insulating layer 118, the pair of high-concentration impurity regions 120a and 120b, and the like (see FIG. 8E). The metal layer 122 can be formed by various film formation methods such as a vacuum evaporation method, a sputtering method, and a spin coating method. The metal layer 122 is preferably formed using a metal material that reacts with a semiconductor material included in the semiconductor region 104 to be a low-resistance metal compound. Examples of such a metal material include titanium, tantalum, tungsten, nickel, cobalt, platinum, and the like.

  Next, heat treatment is performed to react the metal layer 122 with the semiconductor material. Thus, a pair of metal compound regions 124a and 124b in contact with the pair of high concentration impurity regions 120a and 120b is formed (see FIG. 8F). Note that in the case where polycrystalline silicon or the like is used for the gate electrode layer 110a, a metal compound region is also formed in a portion in contact with the metal layer 122 of the gate electrode layer 110a.

  As the heat treatment, for example, heat treatment by flash lamp irradiation can be used. Of course, other heat treatment methods may be used, but in order to improve the controllability of the chemical reaction related to the formation of the metal compound, it is desirable to use a method capable of realizing a heat treatment for a very short time. Note that the metal compound region is formed by a reaction between a metal material and a semiconductor material, and is a region in which conductivity is sufficiently increased. By forming the metal compound region, the electrical resistance can be sufficiently reduced and the device characteristics can be improved. Note that the metal layer 122 is removed after the pair of metal compound regions 124a and 124b is formed.

  Next, an interlayer insulating layer 126 and an interlayer insulating layer 128 are formed so as to cover the components formed in the above steps (see FIG. 8G). The interlayer insulating layer 126 and the interlayer insulating layer 128 can be formed using a material including an inorganic insulating material such as silicon oxide, silicon nitride oxide, silicon nitride, hafnium oxide, aluminum oxide, or tantalum oxide. Alternatively, it can be formed using an organic insulating material such as polyimide or acrylic. Note that although a two-layer structure of the interlayer insulating layer 126 and the interlayer insulating layer 128 is employed here, the structure of the interlayer insulating layer is not limited to this. After the formation of the interlayer insulating layer 128, the surface is preferably planarized by CMP, etching, or the like.

  After that, openings reaching the pair of metal compound regions 124a and 124b are formed in the interlayer insulating layer, and a source electrode layer 130a and a drain electrode layer 130b are formed in the openings (see FIG. 8H). For example, the source electrode layer 130a and the drain electrode layer 130b are formed by forming a conductive layer in a region including an opening using a PVD method, a CVD method, or the like, and then using a method such as etching treatment or CMP to form a part of the conductive layer. It can be formed by removing.

  Note that when the source electrode layer 130a and the drain electrode layer 130b are formed, it is preferable to process the surfaces so as to be flat. For example, when a tungsten film is formed so as to be embedded in the opening after a thin titanium film or titanium nitride film is formed in a region including the opening, unnecessary tungsten, titanium, titanium nitride, or the like is removed by subsequent CMP. At the same time, the flatness of the surface can be improved. In this manner, by planarizing the surface including the source electrode layer 130a and the drain electrode layer 130b, a favorable electrode, wiring, insulating layer, semiconductor layer, or the like can be formed in a later step.

  Note that only the source electrode layer 130a and the drain electrode layer 130b in contact with the pair of metal compound regions 124a and 124b are shown here, but in this step, an electrode layer functioning as a wiring (for example, the electrode layer in FIG. 7). 130c) and the like can be formed together. There is no particular limitation on a material that can be used for the source electrode layer 130a and the drain electrode layer 130b, and various conductive materials can be used. For example, a conductive material such as molybdenum, titanium, chromium, tantalum, tungsten, aluminum, copper, neodymium, or scandium can be used.

  Thus, the P-type transistor 160 using the substrate 100 containing a semiconductor material is formed. Note that an electrode, a wiring, an insulating layer, or the like may be further formed after the above step. A highly integrated circuit can be provided by adopting a multilayer wiring structure formed of a laminated structure of an interlayer insulating layer and a conductive layer as a wiring structure. In addition, an N-type transistor using the substrate 100 including a semiconductor material can be formed through a process similar to the above process. That is, in the above-described process, an N-type transistor can be formed by changing the impurity element added to the semiconductor region to an impurity element such as phosphorus (P) or arsenic (As).

  Next, a process of manufacturing the N-type transistor 164 over the interlayer insulating layer 128 will be described with reference to FIGS. 9 and 10 show various electrode layers on the interlayer insulating layer 128, the manufacturing process of the N-type transistor 164, and the like, so that the P-type transistor 160 and the like existing below the N-type transistor 164 are shown. Is omitted.

  First, the insulating layer 132 is formed over the interlayer insulating layer 128, the source electrode layer 130a, the drain electrode layer 130b, and the electrode layer 130c (see FIG. 9A). The insulating layer 132 can be formed by a PVD method, a CVD method, or the like. Alternatively, the insulating layer can be formed using a material including an inorganic insulating material such as silicon oxide, silicon nitride oxide, silicon nitride, hafnium oxide, aluminum oxide, or tantalum oxide.

  Next, an opening reaching the source electrode layer 130a, the drain electrode layer 130b, and the electrode layer 130c is formed in the insulating layer 132. At this time, an opening is also formed in a region where the gate electrode layer 136d is formed later. Then, a conductive layer 134 is formed so as to be embedded in the opening (see FIG. 9B). The opening can be formed by a method such as etching using a mask. The mask can be formed by a method such as exposure using a photomask. As the etching, either wet etching or dry etching may be used. From the viewpoint of fine processing, it is preferable to use dry etching. The conductive layer 134 can be formed by a film formation method such as a PVD method or a CVD method. As a material that can be used for forming the conductive layer 134, conductive materials such as molybdenum, titanium, chromium, tantalum, tungsten, aluminum, copper, neodymium, and scandium, alloys thereof, compounds (for example, nitrides), and the like can be given. Can be mentioned.

  More specifically, for example, a method in which a titanium film is thinly formed by a PVD method in a region including an opening, a titanium nitride film is thinly formed by a CVD method, and then a tungsten film is formed so as to be embedded in the opening is applied. Can do. Here, the titanium film formed by the PVD method reduces the oxide film at the interface and reduces the contact resistance with the lower electrode layer (here, the source electrode layer 130a, the drain electrode layer 130b, the electrode layer 130c, and the like). It has a function. The titanium nitride film formed thereafter has a barrier function that suppresses diffusion of the conductive material. Further, after forming a barrier film made of titanium, titanium nitride, or the like, a copper film may be formed by a plating method.

  After the conductive layer 134 is formed, a part of the conductive layer 134 is removed by a method such as etching or CMP, the insulating layer 132 is exposed, and the electrode layer 136a, the electrode layer 136b, the electrode layer 136c, and the gate electrode A layer 136d is formed (see FIG. 9C). Note that when the electrode layer 136a, the electrode layer 136b, the electrode layer 136c, and the gate electrode layer 136d are formed by removing part of the conductive layer 134, it is preferable that the surface be processed to be flat. In this manner, by planarizing the surfaces of the insulating layer 132, the electrode layer 136a, the electrode layer 136b, the electrode layer 136c, and the gate electrode layer 136d, a favorable electrode, wiring, insulating layer, semiconductor layer, or the like in a later step. Can be formed.

Next, the gate insulating layer 138 is formed so as to cover the insulating layer 132, the electrode layer 136a, the electrode layer 136b, the electrode layer 136c, and the gate electrode layer 136d (see FIG. 9D). The gate insulating layer 138 can be formed by a CVD method, a sputtering method, or the like. The gate insulating layer 138 is preferably formed to include silicon oxide, silicon nitride, silicon oxynitride, silicon nitride oxide, aluminum oxide, hafnium oxide, tantalum oxide, or the like. Note that the gate insulating layer 138 may have a single-layer structure or a stacked structure. For example, the gate insulating layer 138 made of silicon oxynitride can be formed by a plasma CVD method using silane (SiH ₄ ), oxygen, and nitrogen as a source gas. The thickness of the gate insulating layer 138 is not particularly limited, and can be, for example, not less than 10 nm and not more than 500 nm. In the case of a stacked structure, for example, it is preferable to stack a first gate insulating layer with a thickness of 50 nm to 200 nm and a second gate insulating layer with a thickness of 5 nm to 300 nm on the first gate insulating layer. is there.

  Note that an i-type or substantially i-type oxide semiconductor (a highly purified oxide semiconductor) by removing impurities is extremely sensitive to interface states and interface charges. When such an oxide semiconductor is used for the oxide semiconductor layer, an interface with the gate insulating layer is important. That is, the gate insulating layer 138 in contact with the highly purified oxide semiconductor layer is required to have high quality.

  For example, a high-density plasma CVD method using μ waves (2.45 GHz) is preferable in that a high-quality gate insulating layer 138 with high density and high withstand voltage can be formed. This is because when the highly purified oxide semiconductor layer and the high-quality gate insulating layer are in close contact with each other, the interface state can be reduced and interface characteristics can be improved.

  Of course, as long as a high-quality insulating layer can be formed as the gate insulating layer, another method such as a sputtering method or a plasma CVD method can be applied even when a highly purified oxide semiconductor layer is used. it can. Alternatively, an insulating layer whose film quality and interface characteristics are modified by heat treatment after formation may be used. In any case, the gate insulating layer 138 which has favorable film quality as the gate insulating layer 138, can reduce the interface state density with the oxide semiconductor layer, and can form a favorable interface may be formed.

Further, in an 85 ° C., 2 × 10 ⁶ (V / cm), 12-hour gate bias / thermal stress test (BT test), when impurities are added to an oxide semiconductor, the impurities and the main oxide semiconductor A bond with a component is cut by a strong electric field (B: bias) and a high temperature (T: temperature), and the generated dangling bond induces a threshold voltage (Vth) drift.

  In contrast, an oxide semiconductor impurity, particularly hydrogen or water, is eliminated as much as possible, and the interface characteristics with the gate insulating layer are improved as described above, thereby obtaining a transistor that is stable with respect to the BT test. It is possible.

  Next, an oxide semiconductor layer is formed over the gate insulating layer 138, and the oxide semiconductor layer is processed by a method such as etching using a mask, so that the island-shaped oxide semiconductor layer 140 is formed (FIG. 9). (See (E)).

As the oxide semiconductor layer, an In-Ga-Zn-O-based, In-Sn-Zn-O-based, In-Al-Zn-O-based, Sn-Ga-Zn-O-based, Al-Ga-Zn-O-based layer can be used. -Based, Sn-Al-Zn-O-based, In-Zn-O-based, Sn-Zn-O-based, Al-Zn-O-based, In-O-based, Sn-O-based, and Zn-O-based oxide semiconductors It is preferable to use a layer, particularly an amorphous oxide semiconductor layer. In this embodiment, an amorphous oxide semiconductor layer is formed by a sputtering method using an In—Ga—Zn—O-based metal oxide target as the oxide semiconductor layer. Note that crystallization can be suppressed by adding silicon to the amorphous oxide semiconductor layer. Therefore, for example, an oxide using a target containing 2 wt% or more and 10 wt% or less of SiO ₂ can be used. A semiconductor layer may be formed.

As a target for forming the oxide semiconductor layer by a sputtering method, for example, a metal oxide target containing zinc oxide as a main component can be used. In addition, a metal oxide target containing In, Ga, and Zn (composition ratio: In ₂ O ₃ : Ga ₂ O ₃ : ZnO = 1: 1: 1 [mol ratio], In: Ga: Zn = 1: 1 : 0.5 [atom ratio]) or the like can also be used. In addition, as a metal oxide target containing In, Ga, and Zn, a composition of In: Ga: Zn = 1: 1: 1 [atom ratio] or In: Ga: Zn = 1: 1: 2 [atom ratio] A target having a ratio may be used. The filling rate of the metal oxide target is 90% or more and 100% or less, preferably 95% or more (for example, 99.9%). By using a metal oxide target with a high filling rate, a dense oxide semiconductor layer is formed.

  The atmosphere for forming the oxide semiconductor layer is preferably a rare gas (typically argon) atmosphere, an oxygen atmosphere, or a mixed atmosphere of a rare gas (typically argon) and oxygen. Specifically, for example, it is preferable to use a high-purity gas from which impurities such as hydrogen, water, hydroxyl group, and hydride are removed to about several ppm (preferably about several ppb).

When forming the oxide semiconductor layer, the substrate is held in a treatment chamber kept under reduced pressure, and the substrate temperature is set to 100 ° C. to 600 ° C., preferably 200 ° C. to 400 ° C. By forming the oxide semiconductor layer while heating the substrate, the concentration of impurities contained in the oxide semiconductor layer can be reduced. Further, damage due to sputtering is reduced. Then, a sputtering gas from which hydrogen and water are removed is introduced while moisture remaining in the treatment chamber is removed, and an oxide semiconductor layer is formed using a metal oxide as a target. In order to remove moisture remaining in the treatment chamber, an adsorption-type vacuum pump is preferably used. For example, a cryopump, an ion pump, or a titanium sublimation pump can be used. The exhaust means may be a turbo pump provided with a cold trap. A treatment chamber exhausted using a cryopump exhausts a compound containing hydrogen atoms (more preferably a compound containing carbon atoms) such as hydrogen atoms and water (H ₂ O), for example. The concentration of impurities contained in the formed oxide semiconductor layer can be reduced.

  As the formation conditions, for example, the distance between the substrate and the target is 100 mm, the pressure is 0.6 Pa, the direct current (DC) power is 0.5 kW, and the atmosphere is an oxygen (oxygen flow rate 100%) atmosphere. can do. Note that a pulsed direct current (DC) power source is preferable because powder substances (also referred to as particles or dust) generated in film formation can be reduced and the film thickness can be made uniform. The thickness of the oxide semiconductor layer is 2 nm to 200 nm, preferably 5 nm to 30 nm. Note that an appropriate thickness varies depending on an oxide semiconductor material to be used, and the thickness may be selected as appropriate depending on a material to be used.

  Note that before the oxide semiconductor layer is formed by a sputtering method, it is preferable to perform reverse sputtering in which argon gas is introduced to generate plasma to remove dust attached to the surface of the gate insulating layer 138. is there. Here, reverse sputtering refers to a method in which ions are collided with a sputtering target in normal sputtering, but the surface is modified by colliding ions with a treatment surface. As a method of causing ions to collide with the processing surface, there is a method of generating a plasma near the substrate by applying a high frequency voltage to the processing surface side in an argon atmosphere. Note that nitrogen, helium, oxygen, or the like may be used instead of the argon atmosphere.

  For the etching of the oxide semiconductor layer, either dry etching or wet etching may be used. Of course, both can be used in combination. Etching conditions (such as an etching gas, an etchant, etching time, and temperature) are appropriately set depending on the material so that the film can be etched into a desired shape.

As an etching gas used for dry etching, for example, a gas containing chlorine (chlorine-based gas such as chlorine (Cl ₂ ), boron chloride (BCl ₃ ), silicon chloride (SiCl ₄ ), carbon tetrachloride (CCl ₄ ), or the like is used. and so on. Gas containing fluorine (fluorine-based gas such as carbon tetrafluoride (CF ₄ ), sulfur hexafluoride (SF ₆ ), nitrogen trifluoride (NF ₃ ), trifluoromethane (CHF ₃ ), etc.), bromide Hydrogen (HBr), oxygen (O ₂ ), or a gas obtained by adding a rare gas such as helium (He) or argon (Ar) to these gases may be used.

  As the dry etching method, a parallel plate RIE (Reactive Ion Etching) method or an ICP (Inductively Coupled Plasma) etching method can be used. Etching conditions (such as the amount of power applied to the coil-type electrode, the amount of power applied to the electrode on the substrate side, and the electrode temperature on the substrate side) are set as appropriate so that the film can be etched into a desired shape.

  As an etchant used for wet etching, a mixed solution of phosphoric acid, acetic acid, and nitric acid, or the like can be used. An etching solution such as ITO07N (manufactured by Kanto Chemical Co., Inc.) may be used.

  Next, first heat treatment is preferably performed on the oxide semiconductor layer. By the first heat treatment, the oxide semiconductor layer can be dehydrated or dehydrogenated. The temperature of the first heat treatment is 300 ° C. or higher and 750 ° C. or lower, preferably 400 ° C. or higher and lower than the strain point of the substrate. For example, the substrate is introduced into an electric furnace using a resistance heating element and the oxide semiconductor layer 140 is heat-treated at 450 ° C. for 1 hour in a nitrogen atmosphere. During this time, the oxide semiconductor layer 140 is not exposed to the air so that water and hydrogen are not mixed again.

  Note that the heat treatment apparatus is not limited to an electric furnace, and may be a device for heating an object to be processed by heat conduction or heat radiation from a medium such as a heated gas. For example, a rapid thermal annealing (RTA) device such as a GRTA (Gas Rapid Thermal Anneal) device or an LRTA (Lamp Rapid Thermal Anneal) device can be used. The LRTA apparatus is an apparatus that heats an object to be processed by radiation of light (electromagnetic waves) emitted from a lamp such as a halogen lamp, a metal halide lamp, a xenon arc lamp, a carbon arc lamp, a high pressure sodium lamp, or a high pressure mercury lamp. The GRTA apparatus is an apparatus that performs heat treatment using a high-temperature gas. As the gas, an inert gas that does not react with an object to be processed by heat treatment, such as nitrogen or a rare gas such as argon, is used.

  For example, as the first heat treatment, a GRTA treatment may be performed in which the substrate is put into an inert gas heated to a high temperature of 650 ° C. to 700 ° C., heated for several minutes, and then the substrate is taken out of the inert gas. . When GRTA treatment is used, high-temperature heat treatment can be performed in a short time. Further, since the heat treatment is performed for a short time, it can be applied even under a temperature condition exceeding the strain point of the substrate.

  Note that the first heat treatment is preferably performed in an atmosphere containing nitrogen or a rare gas (such as helium, neon, or argon) as a main component and not containing water, hydrogen, or the like. For example, the purity of nitrogen or a rare gas such as helium, neon, or argon introduced into the heat treatment apparatus is 6N (99.9999%) or more, preferably 7N (99.99999%) or more (that is, the impurity concentration is 1 ppm or less). , Preferably 0.1 ppm or less).

  Depending on the conditions of the first heat treatment or the material of the oxide semiconductor layer, the oxide semiconductor layer may be crystallized to be microcrystalline or polycrystalline. For example, the oxide semiconductor layer may be a microcrystalline oxide semiconductor layer with a crystallization rate of 90% or more, or 80% or more. Further, depending on the conditions of the first heat treatment or the material of the oxide semiconductor layer, an amorphous oxide semiconductor layer which does not include a crystal component may be formed.

  In the case where an oxide semiconductor layer in which microcrystals (particle diameter of 1 nm to 20 nm (typically 2 nm to 4 nm)) are mixed in an amorphous oxide semiconductor (for example, the surface of the oxide semiconductor layer) is used. There is also.

In addition, electrical characteristics of the oxide semiconductor layer can be changed by aligning microcrystals in the amorphous phase. For example, in the case where an oxide semiconductor layer is formed using an In—Ga—Zn—O-based metal oxide target, microcrystals in which crystal grains of In ₂ Ga ₂ ZnO ₇ having electrical anisotropy are oriented are aligned. By forming the portion, the electrical characteristics of the oxide semiconductor layer can be changed.

More specifically, for example, by aligning the c-axis of In ₂ Ga ₂ ZnO ₇ in a direction perpendicular to the surface of the oxide semiconductor layer, conductivity in a direction parallel to the surface of the oxide semiconductor layer is obtained. And the insulating property in the direction perpendicular to the surface of the oxide semiconductor layer can be improved. In addition, such a microcrystalline portion has a function of suppressing entry of impurities such as water and hydrogen into the oxide semiconductor layer.

  Note that the oxide semiconductor layer having the microcrystalline portion can be formed by surface heating of the oxide semiconductor layer by GRTA treatment. In addition, it is possible to form the film more suitably by using a sputtering target having a Zn content smaller than that of In or Ga.

  The first heat treatment for the oxide semiconductor layer 140 can be performed on the oxide semiconductor layer before being processed into the island-shaped oxide semiconductor layer 140. In that case, after the first heat treatment, the substrate is taken out of the heating apparatus and a photolithography process is performed.

  Note that the heat treatment can be referred to as dehydration treatment, dehydrogenation treatment, or the like because it has a dehydration and dehydrogenation effect on the oxide semiconductor layer 140. Such dehydration treatment and dehydrogenation treatment are performed after the oxide semiconductor layer is formed, after the source electrode layer and the drain electrode layer are stacked over the oxide semiconductor layer 140, or on the source electrode layer and the drain electrode layer. After the protective insulating layer is formed, it can be performed at the same timing. Further, such dehydration treatment and dehydrogenation treatment are not limited to one time, and may be performed a plurality of times.

  Next, the source electrode layer 142a and the drain electrode layer 142b are formed so as to be in contact with the oxide semiconductor layer 140 (see FIG. 9F). The source electrode layer 142a and the drain electrode layer 142b can be formed by forming a conductive layer so as to cover the oxide semiconductor layer 140 and then selectively etching the conductive layer.

  The conductive layer can be formed by a PVD method such as a sputtering method or a CVD method such as a plasma CVD method. As a material for the conductive layer, an element selected from aluminum, chromium, copper, tantalum, titanium, molybdenum, and tungsten, an alloy containing the above-described element as a component, or the like can be used. A material selected from one or more of manganese, magnesium, zirconium, beryllium, and thorium may be used. Alternatively, a material obtained by combining one or more elements selected from titanium, tantalum, tungsten, molybdenum, chromium, neodymium, and scandium with aluminum may be used. The conductive layer may have a single layer structure or a stacked structure of two or more layers. For example, a single-layer structure of an aluminum film containing silicon, a two-layer structure in which a titanium film is stacked on an aluminum film, and a three-layer structure in which a titanium film, an aluminum film, and a titanium film are stacked.

  Here, it is preferable to use ultraviolet light, KrF laser light, or ArF laser light for exposure when forming a mask used for etching.

  The channel length (L) of the transistor is determined by the distance between the lower end portion of the source electrode layer 142a and the lower end portion of the drain electrode layer 142b. Note that when exposure with a channel length (L) of less than 25 nm is performed, exposure for mask formation is performed using extreme ultraviolet (Extreme Ultraviolet) having an extremely short wavelength of several nm to several tens of nm. Exposure by extreme ultraviolet light has a high resolution and a large depth of focus. Therefore, the channel length (L) of a transistor to be formed later can be set to 10 nm to 1000 nm, and the operation speed of the circuit can be increased.

  Note that each material and etching conditions are adjusted as appropriate so that the oxide semiconductor layer 140 is not removed when the conductive layer is etched. Note that depending on the material and etching conditions, part of the oxide semiconductor layer 140 may be etched in this step to be an oxide semiconductor layer having a groove (a depressed portion).

  An oxide conductive layer may be formed between the oxide semiconductor layer 140 and the source electrode layer 142a or between the oxide semiconductor layer 140 and the drain electrode layer 142b. The oxide conductive layer and the metal layer for forming the source electrode layer 142a and the drain electrode layer 142b can be formed continuously (continuous film formation). The oxide conductive layer can function as a source region or a drain region. By providing such an oxide conductive layer, resistance of the source region or the drain region can be reduced, so that high-speed operation of the transistor is realized.

  Further, in order to reduce the number of masks used and the number of processes, a resist mask may be formed using a multi-tone mask which is an exposure mask in which transmitted light has a plurality of intensities, and an etching process may be performed using the resist mask. . A resist mask formed using a multi-tone mask has a shape (step shape) having a plurality of thicknesses, and the shape can be further deformed by ashing. Therefore, the resist mask can be used for a plurality of etching processes for processing into different patterns. it can. That is, a resist mask corresponding to at least two kinds of different patterns can be formed using one multi-tone mask. Therefore, the number of exposure masks can be reduced, and the corresponding photolithography process can be reduced, so that the process can be simplified.

Note that plasma treatment using a gas such as N ₂ O, N ₂ , or Ar is preferably performed after the above steps. By the plasma treatment, water or the like attached to the exposed surface of the oxide semiconductor layer is removed. Further, plasma treatment may be performed using a mixed gas of oxygen and argon.

  Next, the protective insulating layer 144 in contact with part of the oxide semiconductor layer 140 is formed without exposure to the air (see FIG. 9G).

  The protective insulating layer 144 can be formed as appropriate by a method such as sputtering, in which an impurity such as water or hydrogen is not mixed into the protective insulating layer 144. The thickness is at least 1 nm or more. Examples of the material that can be used for the protective insulating layer 144 include silicon oxide, silicon nitride, silicon oxynitride, and silicon nitride oxide. Further, the structure may be a single layer structure or a stacked structure. The substrate temperature at the time of forming the protective insulating layer 144 is preferably room temperature to 300 ° C., and the atmosphere is a rare gas (typically argon) atmosphere, an oxygen atmosphere, or a rare gas (typically argon). ) And oxygen in a mixed atmosphere.

  When hydrogen is contained in the protective insulating layer 144, penetration of the hydrogen into the oxide semiconductor layer 140, extraction of oxygen in the oxide semiconductor layer 140 due to hydrogen, or the like occurs, and the back channel side of the oxide semiconductor layer 140 is As a result, the resistance is lowered and a parasitic channel may be formed. Therefore, it is important not to use hydrogen in the formation method so that the protective insulating layer 144 contains as little hydrogen as possible.

  In addition, the protective insulating layer 144 is preferably formed while moisture remaining in the treatment chamber is removed. This is for preventing hydrogen, a hydroxyl group, and moisture from being contained in the oxide semiconductor layer 140 and the protective insulating layer 144.

In order to remove moisture remaining in the treatment chamber, an adsorption-type vacuum pump is preferably used. For example, it is preferable to use a cryopump, an ion pump, or a titanium sublimation pump. The exhaust means may be a turbo pump provided with a cold trap. The treatment chamber evacuated using the cryopump is included in the protective insulating layer 144 formed in the treatment chamber because, for example, hydrogen atoms, compounds containing hydrogen atoms such as water (H ₂ O), and the like are removed. Impurity concentration can be reduced.

  As a sputtering gas used for forming the protective insulating layer 144, a high-purity gas from which impurities such as hydrogen, water, a hydroxyl group, or a hydride are removed to about several ppm (preferably, about several ppb) is used. Is preferred.

  Next, second heat treatment (preferably 200 ° C. to 400 ° C., for example, 250 ° C. to 350 ° C.) is preferably performed in an inert gas atmosphere or an oxygen gas atmosphere. For example, the second heat treatment is performed at 250 ° C. for 1 hour in a nitrogen atmosphere. When the second heat treatment is performed, variation in electrical characteristics of the transistor can be reduced.

  Moreover, you may perform the heat processing for 100 to 200 degreeC and 1 to 30 hours in air | atmosphere. This heat treatment may be performed while maintaining a constant heating temperature, or by repeatedly raising the temperature from room temperature to a heating temperature of 100 ° C. or more and 200 ° C. or less and lowering the temperature from the heating temperature to the room temperature a plurality of times. Also good. Further, this heat treatment may be performed under reduced pressure before the formation of the protective insulating layer. When heat treatment is performed under reduced pressure, the heating time can be shortened. Note that the heat treatment may be performed instead of the second heat treatment, or may be performed before or after the second heat treatment.

  Next, an interlayer insulating layer 146 is formed over the protective insulating layer 144 (see FIG. 10A). The interlayer insulating layer 146 can be formed by a PVD method, a CVD method, or the like. Alternatively, the insulating layer can be formed using a material including an inorganic insulating material such as silicon oxide, silicon nitride oxide, silicon nitride, hafnium oxide, aluminum oxide, or tantalum oxide. After the formation of the interlayer insulating layer 146, the surface is preferably planarized by a method such as CMP or etching.

  Next, openings reaching the electrode layer 136a, the electrode layer 136b, the electrode layer 136c, the source electrode layer 142a, and the drain electrode layer 142b are formed in the interlayer insulating layer 146, the protective insulating layer 144, and the gate insulating layer 138. A conductive layer 148 is formed so as to be embedded in the opening (see FIG. 10B). The opening can be formed by a method such as etching using a mask. The mask can be formed by a method such as exposure using a photomask. As the etching, either wet etching or dry etching may be used. From the viewpoint of fine processing, it is preferable to use dry etching. The conductive layer 148 can be formed by a film formation method such as a PVD method or a CVD method. As a material that can be used for forming the conductive layer 148, a conductive material such as molybdenum, titanium, chromium, tantalum, tungsten, aluminum, copper, neodymium, or scandium, an alloy thereof, a compound (eg, nitride), or the like can be used. Can be mentioned.

  Specifically, for example, a method in which a titanium film is thinly formed in a region including an opening by a PVD method, a titanium nitride film is thinly formed by a CVD method, and then a tungsten film is formed so as to be embedded in the opening is applied. it can. Here, the titanium film formed by the PVD method reduces the oxide film at the interface, and lower electrodes (here, the electrode layer 136a, the electrode layer 136b, the electrode layer 136c, the source electrode layer 142a, and the drain electrode layer 142b) and Has a function of reducing the contact resistance. Further, the titanium nitride film formed thereafter has a barrier function that suppresses diffusion of the conductive material. Further, after forming a barrier film made of titanium, titanium nitride, or the like, a copper film may be formed by a plating method.

  After the conductive layer 148 is formed, a part of the conductive layer 148 is removed by a method such as etching or CMP to expose the interlayer insulating layer 146, and the electrode layer 150a, the electrode layer 150b, the electrode layer 150c, and the electrode layer 150d and an electrode layer 150e are formed (see FIG. 10C). Note that when the electrode layer 150a, the electrode layer 150b, the electrode layer 150c, the electrode layer 150d, and the electrode layer 150e are formed by removing part of the conductive layer 148, the conductive layer 148 may be processed to have a flat surface. desirable. In this manner, by planarizing the surfaces of the interlayer insulating layer 146, the electrode layer 150a, the electrode layer 150b, the electrode layer 150c, the electrode layer 150d, and the electrode layer 150e, a good electrode, wiring, and insulating layer can be obtained in a later step. A semiconductor layer or the like can be formed.

  Further, an insulating layer 152 is formed, and openings that reach the electrode layer 150a, the electrode layer 150b, the electrode layer 150c, the electrode layer 150d, and the electrode layer 150e are formed in the insulating layer 152, and a conductive layer is embedded so as to be embedded in the openings. After the formation, a part of the conductive layer is removed by a method such as etching or CMP, the insulating layer 152 is exposed, and the electrode layer 154a, the electrode layer 154b, the electrode layer 154c, and the electrode layer 154d are formed (FIG. 10 (D)). Since this step is the same as that for forming the electrode layer 150a and the like, details are omitted.

In the case where the N-type transistor 164 is manufactured by the above method, the hydrogen concentration of the oxide semiconductor layer 140 is 5 × 10 ¹⁹ (atoms / cm ³ ) or less, and the leakage current of the N-type transistor 164 can be reduced. become. By applying such an excellent N-type transistor 164 to the semiconductor device described in any of Embodiments 1 to 4, the standby power of the semiconductor device can be reduced.

<Modification>
11 to 14 show modification examples of the configuration of the N-type transistor 164. FIG. That is, the configuration of the P-type transistor 160 is the same as described above.

  FIG. 11 illustrates an N-type transistor 164 having a structure in which a gate electrode layer 136d is provided under the oxide semiconductor layer 140 and the source electrode layer 142a and the drain electrode layer 142b are in contact with each other on the lower side of the oxide semiconductor layer 140. .

  A significant difference between the structure illustrated in FIG. 11 and the structure illustrated in FIG. 7 is a connection position between the source electrode layer 142 a and the drain electrode layer 142 b and the oxide semiconductor layer 140. That is, in the configuration illustrated in FIG. 7, the upper surface of the oxide semiconductor layer 140 is in contact with the source electrode layer 142 a and the drain electrode layer 142 b, whereas in the configuration illustrated in FIG. 11, the lower side of the oxide semiconductor layer 140 , The source electrode layer 142a and the drain electrode layer 142b are in contact with each other. Due to this difference in contact, the arrangement of other electrode layers, insulating layers, and the like is different. Details of each component are the same as those in FIG.

  Specifically, the N-type transistor 164 illustrated in FIG. 11 includes a gate electrode layer 136d provided over the interlayer insulating layer 128, a gate insulating layer 138 provided over the gate electrode layer 136d, and the gate insulating layer 138. A source electrode layer 142a and a drain electrode layer 142b, and an oxide semiconductor layer 140 in contact with the upper surface of the source electrode layer 142a and the drain electrode layer 142b. Further, a protective insulating layer 144 is provided over the N-type transistor 164 so as to cover the oxide semiconductor layer 140.

  FIG. 12 illustrates an N-type transistor 164 including the gate electrode layer 136d over the oxide semiconductor layer 140. Here, FIG. 12A illustrates an example of a structure in which the source electrode layer 142a and the drain electrode layer 142b are in contact with the oxide semiconductor layer 140 on the lower surface of the oxide semiconductor layer 140. FIG. B is a diagram illustrating an example of a structure in which the source electrode layer 142 a and the drain electrode layer 142 b are in contact with the oxide semiconductor layer 140 on the upper surface of the oxide semiconductor layer 140.

  A significant difference between the structure illustrated in FIG. 7 or 11 and the structure illustrated in FIG. 12 is that the gate electrode layer 136 d is provided over the oxide semiconductor layer 140. 12A is significantly different from the structure illustrated in FIG. 12B in that the source electrode layer 142a and the drain electrode layer 142b are formed on either the lower surface or the upper surface of the oxide semiconductor layer 140. It is a point whether to touch in. Due to these differences, the arrangement of other electrode layers, insulating layers, and the like is different. Details of each component are the same as in FIG.

  Specifically, the N-type transistor 164 illustrated in FIG. 12A includes a source electrode layer 142a and a drain electrode layer 142b provided over the interlayer insulating layer 128, and an upper surface of the source electrode layer 142a and the drain electrode layer 142b. An oxide semiconductor layer 140 in contact with the oxide semiconductor layer 140, a gate insulating layer 138 provided over the oxide semiconductor layer 140, and a gate electrode layer 136 d in a region overlapping with the oxide semiconductor layer 140 over the gate insulating layer 138.

  12B includes an oxide semiconductor layer 140 provided over the interlayer insulating layer 128 and a source electrode layer 142a provided so as to be in contact with the upper surface of the oxide semiconductor layer 140. And the drain electrode layer 142b, the oxide semiconductor layer 140, the source electrode layer 142a, the gate insulating layer 138 provided over the drain electrode layer 142b, and the region overlapping with the oxide semiconductor layer 140 over the gate insulating layer 138. And a gate electrode layer 136d provided.

  Note that in the configuration illustrated in FIG. 12, components may be omitted as compared to the configuration illustrated in FIG. 7 (for example, the electrode layer 150 a and the electrode layer 154 a). In this case, a secondary effect of simplifying the manufacturing process can be obtained. Of course, in the configuration shown in FIG. 7 and the like, it is needless to say that components that are not essential can be omitted.

  FIG. 13 shows an N-type transistor 164 having a structure in which the gate electrode layer 136d is provided under the oxide semiconductor layer 140 in the case where the element size is relatively large. In this case, since the requirements for surface flatness and coverage are relatively moderate, it is not necessary to form wirings, electrodes, or the like so as to be embedded in the insulating layer. For example, the gate electrode layer 136d or the like can be formed by performing patterning after the conductive layer is formed.

  A significant difference between the structure illustrated in FIG. 13A and the structure illustrated in FIG. 13B is that the source electrode layer 142a and the drain electrode layer 142b are in contact with each other on the lower surface or the upper surface of the oxide semiconductor layer 140. It is a point. Due to these differences, the arrangement of other electrode layers, insulating layers, and the like is different. Details of each component are the same as in FIG.

  Specifically, the N-type transistor 164 illustrated in FIG. 13A includes a gate electrode layer 136d provided over the interlayer insulating layer 128, a gate insulating layer 138 provided over the gate electrode layer 136d, and gate insulation. The source electrode layer 142a and the drain electrode layer 142b provided over the layer 138 and the oxide semiconductor layer 140 in contact with the upper surface of the source electrode layer 142a and the drain electrode layer 142b are provided.

  13B includes a gate electrode layer 136d provided over the interlayer insulating layer 128, a gate insulating layer 138 provided over the gate electrode layer 136d, and the gate insulating layer 138. The oxide semiconductor layer 140 is provided in a region overlapping with the gate electrode layer 136d, and the source electrode layer 142a and the drain electrode layer 142b are provided so as to be in contact with the upper surface of the oxide semiconductor layer 140.

  In the configuration shown in FIG. 13 as well, the components may be omitted as compared to the configuration shown in FIG. Also in this case, the effect of simplifying the manufacturing process can be obtained.

  FIG. 14 illustrates an N-type transistor 164 having a structure in which the gate electrode layer 136d is provided over the oxide semiconductor layer 140 when the element size is relatively large. Also in this case, since the demand for surface flatness and coverage is relatively moderate, it is not necessary to form wirings, electrodes, or the like so as to be embedded in the insulating layer. For example, the gate electrode layer 136d or the like can be formed by performing patterning after the conductive layer is formed.

  A significant difference between the structure illustrated in FIG. 14A and the structure illustrated in FIG. 14B is that the source electrode layer 142a and the drain electrode layer 142b are in contact with each other on the lower surface or the upper surface of the oxide semiconductor layer 140. It is a point. Due to these differences, the arrangement of other electrode layers, insulating layers, and the like is different. Details of each component are the same as in FIG.

  Specifically, the N-type transistor 164 illustrated in FIG. 14A includes a source electrode layer 142a and a drain electrode layer 142b provided over the interlayer insulating layer 128, and an upper surface of the source electrode layer 142a and the drain electrode layer 142b. Is overlapped with the oxide semiconductor layer 140 in contact with the gate insulating layer 138 provided over the source electrode layer 142a, the drain electrode layer 142b, and the oxide semiconductor layer 140, and the oxide semiconductor layer 140 over the gate insulating layer 138. A gate electrode layer 136d provided in the region.

  14B includes an oxide semiconductor layer 140 provided over the interlayer insulating layer 128 and a source electrode layer 142a provided so as to be in contact with the upper surface of the oxide semiconductor layer 140. And a drain electrode layer 142b, a source electrode layer 142a, a drain electrode layer 142b, a gate insulating layer 138 provided over the oxide semiconductor layer 140, and a region overlapping with the oxide semiconductor layer 140 over the gate insulating layer 138 And a gate electrode layer 136d provided.

  In the configuration illustrated in FIG. 14 as well, the components may be omitted as compared to the configuration illustrated in FIG. Also in this case, the effect of simplifying the manufacturing process can be obtained.

  In this embodiment, the example in which the N-type transistor 164 is stacked over the P-type transistor 160 has been described; however, the structures of the P-type transistor 160 and the N-type transistor 164 are not limited thereto. For example, a P-type transistor and an N-type transistor can be formed on the same plane. Further, the P-type transistor 160 and the N-type transistor 164 may be provided to overlap each other.

  By applying the above-described N-type transistor 164 to the N-type transistor included in the semiconductor device described in any of Embodiments 1 to 4, discharge of the battery in the standby state can be suppressed. That is, the standby power of the semiconductor device can be reduced. In addition, the life of the semiconductor device can be extended by suppressing battery discharge in the standby state.

  Note that the content of this embodiment or part of the content can be freely combined with the content of another embodiment or part of the content.

(Embodiment 6)
In this embodiment, an example of a transistor included in the semiconductor device described in any of Embodiments 1 to 4 will be described. Specifically, an example of a transistor in which a channel formation region is formed using an oxide semiconductor will be described.

  One embodiment of a transistor and a manufacturing method thereof in this embodiment will be described with reference to FIGS.

  FIGS. 15A and 15B illustrate an example of a plan view and a cross-sectional structure of a transistor. A transistor 460 illustrated in FIGS. 15A and 15B is a top-gate transistor.

  15A is a plan view of the top-gate transistor 460, and FIG. 15B is a cross-sectional view taken along line D1-D2 in FIG. 15A.

  The transistor 460 includes an insulating layer 457, a source or drain electrode layer 465a (465a1 and 465a2), an oxide semiconductor layer 462, a source or drain electrode layer 465b, a wiring layer 468, over a substrate 450 having an insulating surface. A gate insulating layer 452 and a gate electrode layer 461 (461a and 461b) are included, and the source or drain electrode layer 465a (465a1 and 465a2) is electrically connected to the wiring layer 464 through the wiring layer 468. Although not illustrated, the source or drain electrode layer 465b is also electrically connected to the wiring layer in an opening provided in the gate insulating layer 452.

  Hereinafter, a process for manufacturing the transistor 460 over the substrate 450 will be described with reference to FIGS.

  First, the insulating layer 457 serving as a base film is formed over the substrate 450 having an insulating surface.

  In this embodiment, a silicon oxide layer is formed as the insulating layer 457 by a sputtering method. A substrate 450 is transferred to a treatment chamber, a sputtering gas containing high-purity oxygen from which hydrogen and moisture are removed, a silicon target or quartz (preferably synthetic quartz) is used, and a silicon oxide is formed as an insulating layer 457 on the substrate 450. Deposit layers. Note that oxygen or a mixed gas of oxygen and argon is used as a sputtering gas.

  For example, the purity is 6N, quartz (preferably synthetic quartz) is used, the substrate temperature is 108 ° C., the distance between the substrate and the target (T-S distance) is 60 mm, the pressure is 0.4 Pa, the high-frequency power source 1. A silicon oxide film is formed by RF sputtering in an atmosphere of 5 kW, oxygen, and argon (oxygen flow rate 25 sccm: argon flow rate 25 sccm = 1: 1). The film thickness is 100 nm. Note that instead of quartz (preferably synthetic quartz), a silicon target can be used as a target for forming a silicon oxide film.

In this case, the insulating layer 457 is preferably formed while moisture remaining in the treatment chamber is removed. This is to prevent the insulating layer 457 from containing hydrogen, a hydroxyl group, or moisture. In the treatment chamber evacuated using a cryopump, for example, hydrogen atoms, a compound containing a compound containing hydrogen atoms such as water (H ₂ O), or the like is exhausted; The concentration of impurities contained can be reduced.

  A sputtering gas used for forming the insulating layer 457 is preferably a high-purity gas from which impurities such as hydrogen, water, a hydroxyl group, or a hydride are removed to about several ppm and several ppb.

  The insulating layer 457 may have a stacked structure, for example, a stack of a nitride insulating layer such as a silicon nitride layer, a silicon nitride oxide layer, an aluminum nitride layer, or an aluminum nitride oxide layer from the substrate 450 side and the oxide insulating layer. It is good also as a structure.

  For example, a silicon nitride layer is formed using a silicon target by introducing a sputtering gas containing high-purity nitrogen from which hydrogen and moisture have been removed between the silicon oxide layer and the substrate. Also in this case, it is preferable to form the silicon nitride layer while removing residual moisture in the treatment chamber, as in the case of the silicon oxide layer.

  Next, a conductive film is formed over the insulating layer 457, a resist mask is formed over the conductive film by a first photolithography step, and selective etching is performed to form the source or drain electrode layers 465a1 and 465a2. After that, the resist mask is removed (see FIG. 16A). Although the source or drain electrode layers 465a1 and 465a2 are illustrated as being divided in the cross-sectional view, they are continuous films. Note that it is preferable that end portions of the formed source electrode layer and drain electrode layer have a tapered shape because coverage with a gate insulating layer stacked thereover is improved.

  As a material of the source electrode layer or the drain electrode layer 465a1, 465a2, an element selected from Al, Cr, Cu, Ta, Ti, Mo, W, an alloy containing the above-described elements as a component, or a combination of the above-described elements Alloy films and the like. Further, a material selected from one or more of manganese, magnesium, zirconium, beryllium, and thorium may be used. The metal conductive film may have a single layer structure or a stacked structure of two or more layers. For example, a single layer structure of an aluminum film containing silicon, a two-layer structure in which a titanium film is stacked on an aluminum film, a Ti film, an aluminum film stacked on the Ti film, and a Ti film formed on the Ti film. Examples include a three-layer structure. A single element or a combination of elements selected from titanium (Ti), tantalum (Ta), tungsten (W), molybdenum (Mo), chromium (Cr), neodymium (Nd), and scandium (Sc) is added to Al. A film, an alloy film, or a nitride film may be used.

  In this embodiment, a 150-nm-thick titanium film is formed by a sputtering method as the source or drain electrode layers 465a1 and 465a2.

  Next, an oxide semiconductor film with a thickness of 2 nm to 200 nm is formed over the insulating layer 457 and the source or drain electrode layers 465a1 and 465a2.

  Next, the island-shaped oxide semiconductor layer 462 is processed by a second photolithography process (see FIG. 16B). In this embodiment, the oxide semiconductor film is formed by a sputtering method using an In—Ga—Zn—O-based metal oxide target.

The oxide semiconductor film holds the substrate in a treatment chamber kept under reduced pressure, introduces a sputtering gas from which hydrogen and moisture are removed while removing residual moisture in the treatment chamber, and uses a metal oxide as a target to form the substrate 450. An oxide semiconductor film is formed over the top. In order to remove moisture remaining in the treatment chamber, an adsorption-type vacuum pump is preferably used. For example, it is preferable to use a cryopump, an ion pump, or a titanium sublimation pump. The exhaust means may be a turbo pump provided with a cold trap. A treatment chamber exhausted using a cryopump exhausts, for example, a compound containing hydrogen atoms (more preferably a compound containing carbon atoms) such as a hydrogen atom or water (H ₂ O). The concentration of impurities contained in the formed oxide semiconductor film can be reduced. Further, the substrate may be heated when the oxide semiconductor film is formed.

  As a sputtering gas used for forming the oxide semiconductor film, a high-purity gas from which impurities such as hydrogen, water, a hydroxyl group, or hydride are removed to about several ppm and several ppb is preferably used.

  As an example of the film forming conditions, the substrate temperature is room temperature, the distance between the substrate and the target is 60 mm, the pressure is 0.4 Pa, the direct current (DC) power supply is 0.5 kW, oxygen and argon (oxygen flow rate 15 sccm: argon flow rate 30 sccm). The following conditions apply: Note that a pulse direct current (DC) power source is preferable because powder substances (also referred to as particles or dust) generated in film formation can be reduced and the film thickness can be made uniform. The oxide semiconductor film is preferably 5 nm to 30 nm. Note that an appropriate thickness differs depending on an oxide semiconductor material to be used, and the thickness may be selected as appropriate depending on the material.

  In this embodiment, the oxide semiconductor film is processed into the island-shaped oxide semiconductor layer 462 by a wet etching method using a mixed solution of phosphoric acid, acetic acid, and nitric acid as an etchant.

  In this embodiment, first heat treatment is performed on the oxide semiconductor layer 462. The temperature of the first heat treatment is 400 ° C. or higher and 750 ° C. or lower, preferably 400 ° C. or higher and lower than the strain point of the substrate. Here, a substrate is introduced into an electric furnace which is one of heat treatment apparatuses, and the oxide semiconductor layer is subjected to heat treatment at 450 ° C. for 1 hour in a nitrogen atmosphere, and then the oxide semiconductor layer is exposed to the atmosphere without being exposed to air. An oxide semiconductor layer is obtained by preventing re-mixing of water and hydrogen into the semiconductor layer. Through the first heat treatment, the oxide semiconductor layer 462 can be dehydrated or dehydrogenated.

  Note that the heat treatment apparatus is not limited to an electric furnace, and may include a device for heating an object to be processed by heat conduction or heat radiation from a heating element such as a resistance heating element. For example, a rapid thermal annealing (RTA) device such as a GRTA (Gas Rapid Thermal Anneal) device or an LRTA (Lamp Rapid Thermal Anneal) device can be used. For example, as the first heat treatment, the substrate is moved into an inert gas heated to a high temperature of 650 ° C. to 700 ° C., heated for several minutes, and then moved to a high temperature by moving the substrate to a high temperature. GRTA may be performed from When GRTA is used, high-temperature heat treatment can be performed in a short time.

  Note that in the first heat treatment, it is preferable that water, hydrogen, or the like be not contained in nitrogen or a rare gas such as helium, neon, or argon. Alternatively, the purity of nitrogen or a rare gas such as helium, neon, or argon introduced into the heat treatment apparatus is 6N (99.9999%) or more, preferably 7N (99.99999%) or more (that is, the impurity concentration is 1 ppm). Or less, preferably 0.1 ppm or less).

  Depending on the conditions of the first heat treatment or the material of the oxide semiconductor layer, the material may crystallize into a microcrystalline film or a polycrystalline film.

  The first heat treatment of the oxide semiconductor layer can be performed on the oxide semiconductor film before being processed into the island-shaped oxide semiconductor layer. In that case, after the first heat treatment, the substrate is taken out of the heating apparatus and a photolithography process is performed.

  The heat treatment that exerts the effect of dehydration and dehydrogenation on the oxide semiconductor layer is performed by forming a source electrode and a drain electrode after stacking a source electrode and a drain electrode on the oxide semiconductor layer after forming the oxide semiconductor layer. Any of the steps may be performed after the gate insulating layer is formed thereon.

  Next, a conductive film is formed over the insulating layer 457 and the oxide semiconductor layer 462, a resist mask is formed over the conductive film by a third photolithography step, and selective etching is performed, so that a source electrode layer or a drain electrode is formed. After the layer 465b and the wiring layer 468 are formed, the resist mask is removed (see FIG. 16C). The source or drain electrode layer 465b and the wiring layer 468 may be formed using the same material and process as the source or drain electrode layers 465a1 and 465a2.

  In this embodiment, a 150-nm-thick titanium film is formed by a sputtering method as the source or drain electrode layer 465b and the wiring layer 468. In this embodiment, since the same titanium film is used for the source or drain electrode layers 465a1 and 465a2 and the source or drain electrode layer 465b, the source or drain electrode layers 465a1 and 465a2 and the source electrode layer or The etching cannot be performed with respect to the drain electrode layer 465b in etching. Therefore, a wiring is formed over the source or drain electrode layer 465a2 that is not covered with the oxide semiconductor layer 462 so that the source or drain electrode layer 465a1 and 465a2 are not etched when the source or drain electrode layer 465b is etched. A layer 468 is provided. When different materials having a high selection ratio are used for the source or drain electrode layers 465a1 and 465a2 and the source or drain electrode layer 465b in the etching step, the source or drain electrode layer 465a2 is protected at the time of etching. The wiring layer 468 is not necessarily provided.

  Note that each material and etching conditions are adjusted as appropriate so that the oxide semiconductor layer 462 is not removed when the conductive film is etched.

  In this embodiment, a Ti film is used as the conductive film, an In—Ga—Zn—O-based oxide semiconductor is used for the oxide semiconductor layer 462, and ammonia overwater (ammonia, water, hydrogen peroxide) is used as the etchant. Water mixture).

  Note that in the third photolithography step, only part of the oxide semiconductor layer 462 is etched, whereby an oxide semiconductor layer having a groove (a depressed portion) may be formed. Further, a resist mask for forming the source or drain electrode layer 465b and the wiring layer 468 may be formed by an inkjet method. When the resist mask is formed by an ink-jet method, a manufacturing cost can be reduced because a photomask is not used.

  Next, the gate insulating layer 452 is formed over the insulating layer 457, the oxide semiconductor layer 462, the source or drain electrode layers 465a1 and 465a2, the source or drain electrode layer 465b, and the wiring layer 468.

  The gate insulating layer 452 is formed by a single layer or a stack of silicon oxide layers, silicon nitride layers, silicon oxynitride layers, silicon nitride oxide layers, or aluminum oxide layers by a plasma CVD method, a sputtering method, or the like. Can do. Note that the gate insulating layer 452 is preferably formed by a sputtering method so that the gate insulating layer 452 does not contain a large amount of hydrogen. In the case of forming a silicon oxide film by a sputtering method, a silicon target or a quartz target is used as a target, and oxygen or a mixed gas of oxygen and argon is used as a sputtering gas.

  The gate insulating layer 452 can have a structure in which a silicon oxide layer and a silicon nitride layer are stacked from the source or drain electrode layers 465a1 and 465a2 and the source or drain electrode layer 465b side. In this embodiment, a silicon oxide layer with a thickness of 100 nm is formed by RF sputtering in an atmosphere of pressure 0.4 Pa, high-frequency power supply 1.5 kW, oxygen and argon (oxygen flow rate 25 sccm: argon flow rate 25 sccm = 1: 1). .

  Next, a resist mask is formed by a fourth photolithography step, and selective etching is performed to remove part of the gate insulating layer 452, so that an opening 423 reaching the wiring layer 468 is formed (FIG. 16D). reference). Although not illustrated, an opening reaching the source or drain electrode layer 465b may be formed when the opening 423 is formed. In this embodiment, the opening to the source or drain electrode layer 465b is formed after an interlayer insulating layer is further stacked, and an electrically connected wiring layer is formed in the opening.

  Next, after a conductive film is formed over the gate insulating layer 452 and the opening 423, a gate electrode layer 461 (461a and 461b) and a wiring layer 464 are formed by a fifth photolithography step. Note that the resist mask may be formed by an inkjet method. When the resist mask is formed by an ink-jet method, a manufacturing cost can be reduced because a photomask is not used.

  The material of the gate electrode layer 461 (461a, 461b) and the wiring layer 464 is a metal material such as molybdenum, titanium, chromium, tantalum, tungsten, aluminum, copper, neodymium, scandium, or an alloy material containing these as a main component. And can be formed in a single layer or stacked layers.

  In this embodiment, a 150-nm-thick titanium film is formed by a sputtering method as the gate electrode layers 461 (461a and 461b) and the wiring layer 464.

  Next, second heat treatment (preferably 200 ° C. to 400 ° C., for example, 250 ° C. to 350 ° C.) is performed in an inert gas atmosphere or an oxygen gas atmosphere. In this embodiment, the second heat treatment is performed at 250 ° C. for one hour in a nitrogen atmosphere. The second heat treatment may be performed after a protective insulating layer or a planarization insulating layer is formed over the transistor 460.

  Further, heat treatment may be performed at 100 ° C. to 200 ° C. for 1 hour to 30 hours in the air. This heat treatment may be performed while maintaining a constant heating temperature, or the temperature is raised from room temperature to a heating temperature of 100 ° C. or more and 200 ° C. or less, and the temperature lowering from the heating temperature to the room temperature is repeated several times. May be. Further, this heat treatment may be performed under reduced pressure before formation of the oxide insulating layer. When the heat treatment is performed under reduced pressure, the heating time can be shortened.

  Through the above steps, the transistor 460 including the oxide semiconductor layer 462 in which the concentration of hydrogen, moisture, hydride, or hydroxide is reduced can be formed (see FIG. 16E).

  Further, a protective insulating layer or a planarization insulating layer for planarization may be provided over the transistor 460. Although not illustrated, an opening reaching the source or drain electrode layer 465b is formed in the gate insulating layer 452, the protective insulating layer, or the planarization insulating layer, and the source electrode or the drain electrode layer 465b is electrically connected to the opening. A wiring layer connected to is formed.

  When the oxide semiconductor film is formed as described above, residual moisture in the reaction atmosphere is removed, whereby the concentration of hydrogen and hydride in the oxide semiconductor film can be reduced. Accordingly, stabilization of the oxide semiconductor film can be achieved.

  By applying the above transistor to the transistor included in the semiconductor device described in any of Embodiments 1 to 4, discharge of the battery in the standby state can be suppressed. That is, the standby power of the semiconductor device can be reduced. In addition, the life of the semiconductor device can be extended by suppressing battery discharge in the standby state.

  Further, by forming all of the transistors included in the semiconductor device described in any of Embodiments 1 to 4 using the transistor of this embodiment, a manufacturing process can be reduced, yield can be improved, and manufacturing cost can be reduced. .

  Note that the content of this embodiment or part of the content can be freely combined with the content of another embodiment or part of the content.

(Embodiment 7)
In this embodiment, an example of a transistor included in the semiconductor device described in any of Embodiments 1 to 4 will be described. Specifically, an example of a transistor in which a channel formation region is formed using an oxide semiconductor will be described.

  One embodiment of the transistor of this embodiment and a manufacturing method thereof will be described with reference to FIGS.

  FIGS. 17A to 17E illustrate an example of a cross-sectional structure of a transistor. A transistor 390 illustrated in FIGS. 17A to 17E has a bottom-gate structure and is also referred to as an inverted staggered transistor.

  Although the transistor 390 is described as a single-gate transistor, a multi-gate transistor including a plurality of channel formation regions can be formed as needed.

  Hereinafter, a process for manufacturing the transistor 390 over the substrate 394 will be described with reference to FIGS.

  First, after a conductive film is formed over the substrate 394 having an insulating surface, a gate electrode layer 391 is formed by a first photolithography process. It is preferable that the end portion of the formed gate electrode layer 391 has a tapered shape because coverage with a gate insulating layer stacked thereover is improved. Note that the resist mask may be formed by an inkjet method. When the resist mask is formed by an ink-jet method, a manufacturing cost can be reduced because a photomask is not used.

  There is no particular limitation on a substrate that can be used as the substrate 394 having an insulating surface as long as it has heat resistance enough to withstand heat treatment performed later. A glass substrate such as barium borosilicate glass or alumino borosilicate glass can be used.

As the glass substrate, a glass substrate having a strain point of 730 ° C. or higher is preferably used when the temperature of the subsequent heat treatment is high. For the glass substrate, for example, a glass material such as aluminosilicate glass, aluminoborosilicate glass, or barium borosilicate glass is used. Generally, a more practical heat-resistant glass can be obtained by containing more barium oxide (BaO) than boron oxide. For this reason, it is preferable to use a glass substrate containing more BaO than B ₂ O _3.

  Note that a substrate formed of an insulator such as a ceramic substrate, a quartz substrate, or a sapphire substrate may be used instead of the glass substrate. In addition, a crystallized glass substrate or the like can be used. A plastic substrate or the like can also be used as appropriate.

  An insulating film serving as a base film may be provided between the substrate 394 and the gate electrode layer 391. The base film has a function of preventing diffusion of an impurity element from the substrate 394 and has a stacked structure including one or more films selected from a silicon nitride film, a silicon oxide film, a silicon nitride oxide film, and a silicon oxynitride film. Can be formed.

  The gate electrode layer 391 is formed of a single layer or stacked layers using a metal material such as molybdenum, titanium, chromium, tantalum, tungsten, aluminum, copper, neodymium, or scandium, or an alloy material containing these materials as a main component. Can be formed.

  For example, the two-layer structure of the gate electrode layer 391 includes a two-layer structure in which a molybdenum layer is stacked on an aluminum layer, a two-layer structure in which a molybdenum layer is stacked on a copper layer, and titanium nitride on a copper layer. A two-layer structure in which layers or tantalum nitrides are stacked, a two-layer structure in which titanium nitride layers and molybdenum layers are stacked, or a two-layer structure in which tungsten nitride layers and tungsten layers are stacked are preferable. The three-layer structure is preferably a stack in which a tungsten layer or tungsten nitride, an alloy of aluminum and silicon or an alloy of aluminum and titanium, and a titanium nitride or titanium layer are stacked. Note that the gate electrode layer can be formed using a light-transmitting conductive film. As the light-transmitting conductive film, a light-transmitting conductive oxide film or the like can be given as an example.

  Next, a gate insulating layer 397 is formed over the gate electrode layer 391.

  The gate insulating layer 397 is formed by a single layer or a stack of silicon oxide layers, silicon nitride layers, silicon oxynitride layers, silicon nitride oxide layers, or aluminum oxide layers by a plasma CVD method, a sputtering method, or the like. Can do. Note that the gate insulating layer 397 is preferably formed by a sputtering method so that the gate insulating layer 397 does not contain a large amount of hydrogen. In the case of forming a silicon oxide film by a sputtering method, a silicon target or a quartz target is used as a target, and oxygen or a mixed gas of oxygen and argon is used as a sputtering gas.

The gate insulating layer 397 can have a structure in which a silicon nitride layer and a silicon oxide layer are stacked from the gate electrode layer 391 side. For example, a silicon nitride layer (SiN _y (y> 0)) with a thickness of 50 nm to 200 nm is formed as the first gate insulating layer by a sputtering method, and the second gate insulating layer is formed over the first gate insulating layer. A silicon oxide layer (SiO _x (x> 0)) with a thickness of 5 nm to 300 nm is stacked to form a gate insulating layer.

  In order to prevent hydrogen, a hydroxyl group, and moisture from being contained in the gate insulating layer 397 and the oxide semiconductor film 393 as much as possible, a gate electrode layer 391 is formed in a preheating chamber of a sputtering apparatus as a pretreatment for film formation. It is preferable to preheat the substrate 394 over which the substrate 394 or the gate insulating layer 397 is formed, and to desorb and exhaust impurities such as hydrogen and moisture adsorbed on the substrate 394. Note that the preheating temperature is 100 ° C. or higher and 400 ° C. or lower, preferably 150 ° C. or higher and 300 ° C. or lower. Note that a cryopump is preferable as an exhaustion unit provided in the preheating chamber. Note that this preheating treatment can be omitted. Further, this preheating may be similarly performed on the substrate 394 over which the source electrode layer 395a and the drain electrode layer 395b are formed before the oxide insulating layer 396 is formed.

  Next, an oxide semiconductor film 393 with a thickness greater than or equal to 2 nm and less than or equal to 200 nm is formed over the gate insulating layer 397 (see FIG. 17A).

  Note that before the oxide semiconductor film 393 is formed by a sputtering method, reverse sputtering that generates plasma by introducing argon gas is preferably performed to remove dust attached to the surface of the gate insulating layer 397. . Reverse sputtering is a method of modifying the surface by forming a plasma near the substrate by applying a voltage using an RF power source on the substrate side in an argon atmosphere without applying a voltage to the target side. Note that nitrogen, helium, oxygen, or the like may be used instead of the argon atmosphere.

The oxide semiconductor film 393 is formed by a sputtering method. The oxide semiconductor film 393 includes In—Ga—Zn—O, In—Sn—Zn—O, In—Al—Zn—O, Sn—Ga—Zn—O, and Al—Ga—Zn—O. -Based, Sn-Al-Zn-O-based, In-Zn-O-based, Sn-Zn-O-based, Al-Zn-O-based, In-O-based, Sn-O-based, and Zn-O-based oxide semiconductors Use a membrane. In this embodiment, the oxide semiconductor film 393 is formed by a sputtering method with the use of an In—Ga—Zn—O-based metal oxide target. The oxide semiconductor film 393 can be formed by a sputtering method in a rare gas (typically argon) atmosphere, an oxygen atmosphere, or a rare gas (typically argon) and oxygen atmosphere. In the case where the sputtering method is used, the film may be formed using a target containing 2 wt% or more and 10 wt% or less of SiO ₂ .

As a target for forming the oxide semiconductor film 393 by a sputtering method, a metal oxide target containing zinc oxide as a main component can be used. As another example of the metal oxide target, a metal oxide target containing In, Ga, and Zn (composition ratio: In ₂ O ₃ : Ga ₂ O ₃ : ZnO = 1: 1: 1 [mol Ratio], In: Ga: Zn = 1: 1: 0.5 [atom ratio]). In addition, as a metal oxide target containing In, Ga, and Zn, a composition of In: Ga: Zn = 1: 1: 1 [atom ratio] or In: Ga: Zn = 1: 1: 2 [atom ratio] A target having a ratio can also be used. The filling rate of the metal oxide target is 90% to 100%, preferably 95% to 99.9%. By using a metal oxide target with a high filling rate, the formed oxide semiconductor film becomes a dense film.

The substrate is held in a processing chamber held under reduced pressure, and the substrate is heated to a temperature of room temperature or higher and lower than 400 ° C. Then, a sputtering gas from which hydrogen and moisture are removed is introduced while moisture remaining in the treatment chamber is removed, and the oxide semiconductor film 393 is formed over the substrate 394 using a metal oxide as a target. In order to remove moisture remaining in the treatment chamber, an adsorption-type vacuum pump is preferably used. For example, it is preferable to use a cryopump, an ion pump, or a titanium sublimation pump. The exhaust means may be a turbo pump provided with a cold trap. A treatment chamber exhausted using a cryopump exhausts, for example, a compound containing hydrogen atoms (more preferably a compound containing carbon atoms) such as a hydrogen atom or water (H ₂ O). The concentration of impurities contained in the formed oxide semiconductor film can be reduced. Further, by performing sputtering film formation while removing moisture remaining in the treatment chamber with a cryopump, the substrate temperature in forming the oxide semiconductor film 393 can be reduced from room temperature to lower than 400 ° C.

  As an example of the film forming conditions, the distance between the substrate and the target is 100 mm, the pressure is 0.6 Pa, the direct current (DC) power source is 0.5 kW, and the oxygen (oxygen flow rate is 100%) atmosphere is applied. Note that a pulse direct current (DC) power source is preferable because powder substances (also referred to as particles or dust) generated in film formation can be reduced and the film thickness can be made uniform. The oxide semiconductor film is preferably 5 nm to 30 nm. Note that an appropriate thickness differs depending on an oxide semiconductor material to be used, and the thickness may be selected as appropriate depending on the material.

  As the sputtering method, there are an RF sputtering method using a high frequency power source as a sputtering power source and a DC sputtering method, and a pulse DC sputtering method for applying a bias in a pulsed manner. The RF sputtering method is mainly used when an insulating film is formed, and the DC sputtering method is mainly used when a metal film is formed.

  There is also a multi-source sputtering apparatus in which a plurality of targets of different materials can be installed. The multi-source sputtering apparatus can be formed by stacking different material films in the same chamber, or by simultaneously discharging a plurality of types of materials in the same chamber.

  Further, there are a sputtering apparatus using a magnetron sputtering method having a magnet mechanism inside a chamber, and a sputtering apparatus using an ECR sputtering method using plasma generated using microwaves without using glow discharge.

  In addition, as a film formation method using a sputtering method, a reactive sputtering method in which a target material and a sputtering gas component are chemically reacted during film formation to form a compound thin film thereof, or a voltage is applied to the substrate during film formation. There is also a bias sputtering method.

  Next, the oxide semiconductor film is processed into an island-shaped oxide semiconductor layer 399 by a second photolithography process (see FIG. 17B). Further, a resist mask for forming the island-shaped oxide semiconductor layer 399 may be formed by an inkjet method. When the resist mask is formed by an ink-jet method, a manufacturing cost can be reduced because a photomask is not used.

  In the case of forming a contact hole in the gate insulating layer 397, the step can be performed when the oxide semiconductor layer 399 is formed.

  Note that the etching of the oxide semiconductor film 393 may be dry etching or wet etching, or both may be used.

As an etching gas used for dry etching, a gas containing chlorine (chlorine-based gas such as chlorine (Cl ₂ ), boron chloride (BCl ₃ ), silicon chloride (SiCl ₄ ), carbon tetrachloride (CCl ₄ ), or the like) is preferable. .

Gas containing fluorine (fluorine-based gas such as carbon tetrafluoride (CF ₄ ), sulfur hexafluoride (SF ₆ ), nitrogen trifluoride (NF ₃ ), trifluoromethane (CHF ₃ ), etc.), bromide Hydrogen (HBr), oxygen (O ₂ ), a gas obtained by adding a rare gas such as helium (He) or argon (Ar) to these gases, or the like can be used.

  As the dry etching method, a parallel plate RIE (Reactive Ion Etching) method or an ICP (Inductively Coupled Plasma) etching method can be used. Etching conditions (such as the amount of power applied to the coil-type electrode, the amount of power applied to the substrate-side electrode, the substrate-side electrode temperature, etc.) are adjusted as appropriate so that the desired processed shape can be etched.

  As an etchant used for wet etching, a mixed solution of phosphoric acid, acetic acid, and nitric acid, or the like can be used. In addition, ITO07N (manufactured by Kanto Chemical Co., Inc.) may be used.

  In addition, the etchant after the wet etching is removed by cleaning together with the etched material. The waste solution of the etching solution containing the removed material may be purified and the contained material may be reused. By recovering and reusing materials such as indium contained in the oxide semiconductor layer from the waste liquid after the etching, resources can be effectively used and costs can be reduced.

  Etching conditions (such as an etchant, etching time, and temperature) are adjusted as appropriate depending on the material so that the material can be etched into a desired shape.

  Note that before the conductive film in the next step is formed, reverse sputtering is preferably performed to remove a resist residue or the like attached to the surfaces of the oxide semiconductor layer 399 and the gate insulating layer 397.

  Next, a conductive film is formed over the gate insulating layer 397 and the oxide semiconductor layer 399. The conductive film may be formed by a sputtering method or a vacuum evaporation method. Examples of the material for the conductive film include an element selected from Al, Cr, Cu, Ta, Ti, Mo, and W, an alloy containing the above-described elements as a component, or an alloy film combining the above-described elements. Further, a material selected from one or more of manganese, magnesium, zirconium, beryllium, and thorium may be used. The metal conductive film may have a single layer structure or a stacked structure of two or more layers. For example, a single layer structure of an aluminum film containing silicon, a two-layer structure in which a titanium film is stacked on an aluminum film, a Ti film, an aluminum film stacked on the Ti film, and a Ti film formed on the Ti film. Examples include a three-layer structure. A single element or a combination of elements selected from titanium (Ti), tantalum (Ta), tungsten (W), molybdenum (Mo), chromium (Cr), neodymium (Nd), and scandium (Sc) is added to Al. A film, an alloy film, or a nitride film may be used.

  A resist mask is formed over the conductive film by a third photolithography step, and selective etching is performed to form the source electrode layer 395a and the drain electrode layer 395b, and then the resist mask is removed (see FIG. 17C). ).

  Ultraviolet light, KrF laser light, or ArF laser light is used for light exposure for forming the resist mask in the third photolithography process. A channel length L of a transistor to be formed later is determined by a gap width between the lower end portion of the source electrode layer adjacent to the oxide semiconductor layer 399 and the lower end portion of the drain electrode layer. Note that when exposure is performed with a channel length L of less than 25 nm, exposure at the time of forming a resist mask in the third photolithography process is performed using extreme ultraviolet (Extreme Ultraviolet) having a wavelength as short as several nm to several tens of nm. Do. Exposure by extreme ultraviolet light has a high resolution and a large depth of focus. Accordingly, the channel length L of a transistor to be formed later can be set to 10 nm to 1000 nm, the operation speed of the circuit can be increased, and the off-state current value is extremely small, so that power consumption can be reduced. it can.

  Note that each material and etching conditions are adjusted as appropriate so that the oxide semiconductor layer 399 is not removed when the conductive film is etched.

  In this embodiment, a Ti film is used as the conductive film, an In—Ga—Zn—O-based oxide semiconductor is used for the oxide semiconductor layer 399, and ammonia overwater (ammonia, water, hydrogen peroxide) is used as the etchant. Water mixture).

  Note that in the third photolithography step, only part of the oxide semiconductor layer 399 is etched, whereby an oxide semiconductor layer having a groove (a depressed portion) may be formed. Further, a resist mask for forming the source electrode layer 395a and the drain electrode layer 395b may be formed by an inkjet method. When the resist mask is formed by an ink-jet method, a manufacturing cost can be reduced because a photomask is not used.

  In order to reduce the number of photomasks used in the photolithography process and the number of processes, the etching process may be performed using a resist mask formed by a multi-tone mask that is an exposure mask in which transmitted light has a plurality of intensities. Good. A resist mask formed using a multi-tone mask has a shape with a plurality of thicknesses, and the shape can be further deformed by etching. Therefore, the resist mask can be used for a plurality of etching processes for processing into different patterns. . Therefore, a resist mask corresponding to at least two kinds of different patterns can be formed by using one multi-tone mask. Therefore, the number of exposure masks can be reduced, and the corresponding photolithography process can be reduced, so that the process can be simplified.

The adsorbed water attached to the surface of the oxide semiconductor layer exposed by plasma treatment using a gas such as N ₂ O, N ₂ , or Ar may be removed. Further, plasma treatment may be performed using a mixed gas of oxygen and argon.

  In the case where plasma treatment is performed, the oxide insulating layer 396 is formed as an oxide insulating layer which serves as a protective insulating film in contact with part of the oxide semiconductor layer without being exposed to the air (see FIG. 17D). In this embodiment, the oxide semiconductor layer 399 is formed in contact with the oxide insulating layer 396 in a region where the oxide semiconductor layer 399 does not overlap with the source electrode layer 395a and the drain electrode layer 395b.

  In this embodiment, the substrate 394 including the island-shaped oxide semiconductor layer 399, the source electrode layer 395a, and the drain electrode layer 395b as the oxide insulating layer 396 is heated to a temperature higher than or equal to room temperature and lower than 100 ° C. A sputtering gas containing high-purity oxygen from which moisture has been removed is introduced, and a silicon oxide layer containing defects is formed using a silicon target.

  For example, a silicon target (resistance value: 0.01 Ωcm) having a purity of 6N and doped with boron is used, the distance between the substrate and the target (distance between TS) is 89 mm, the pressure is 0.4 Pa, and the direct current ( DC) A silicon oxide layer is formed by a pulsed DC sputtering method in a power source of 6 kW and in an atmosphere of oxygen (oxygen flow rate 100%). The film thickness is 300 nm. Note that quartz (preferably synthetic quartz) can be used instead of the silicon target as a target for forming the silicon oxide layer. Note that oxygen or a mixed gas of oxygen and argon is used as a sputtering gas.

  In this case, the oxide insulating layer 396 is preferably formed while moisture remaining in the treatment chamber is removed. This is for preventing hydrogen, a hydroxyl group, and moisture from being contained in the oxide semiconductor layer 399 and the oxide insulating layer 396.

In order to remove moisture remaining in the treatment chamber, an adsorption-type vacuum pump is preferably used. For example, it is preferable to use a cryopump, an ion pump, or a titanium sublimation pump. The exhaust means may be a turbo pump provided with a cold trap. The treatment chamber evacuated using a cryopump is included in the oxide insulating layer 396 formed in the treatment chamber, for example, because hydrogen atoms, compounds containing hydrogen atoms such as water (H ₂ O), and the like are exhausted. The concentration of impurities to be reduced can be reduced.

  Note that as the oxide insulating layer 396, a silicon oxynitride layer, an aluminum oxide layer, an aluminum oxynitride layer, or the like can be used instead of the silicon oxide layer.

  Further, heat treatment may be performed at 100 ° C. to 400 ° C. with the oxide insulating layer 396 and the oxide semiconductor layer 399 being in contact with each other. Since the oxide insulating layer 396 in this embodiment includes many defects, impurities such as hydrogen, moisture, hydroxyl, or hydride contained in the oxide semiconductor layer 399 are diffused in the oxide insulating layer 396 by this heat treatment. The impurities contained in the oxide semiconductor layer 399 can be further reduced.

  Through the above steps, the transistor 390 including the oxide semiconductor layer 392 in which the concentration of hydrogen, moisture, hydroxyl, or hydride is reduced can be formed (see FIG. 17E).

  When the oxide semiconductor film is formed as described above, residual moisture in the reaction atmosphere is removed, whereby the concentration of hydrogen and hydride in the oxide semiconductor film can be reduced. Accordingly, stabilization of the oxide semiconductor film can be achieved.

  A protective insulating layer may be provided over the oxide insulating layer. In this embodiment, the protective insulating layer 398 is formed over the oxide insulating layer 396. As the protective insulating layer 398, a silicon nitride film, a silicon nitride oxide film, an aluminum nitride film, an aluminum nitride oxide film, or the like is used.

  As the protective insulating layer 398, the substrate 394 formed up to the oxide insulating layer 396 is heated to a temperature of 100 ° C. to 400 ° C., a sputtering gas containing high-purity nitrogen from which hydrogen and moisture are removed is introduced, and a silicon target is used. A silicon nitride film is formed. In this case as well, like the oxide insulating layer 396, it is preferable to form the protective insulating layer 398 while removing moisture remaining in the treatment chamber.

  In the case where the protective insulating layer 398 is formed, hydrogen or moisture contained in the oxide semiconductor layer is diffused into the oxide insulating layer by heating the substrate 394 to 100 ° C. to 400 ° C. when the protective insulating layer 398 is formed. be able to. In this case, heat treatment is not necessarily performed after the oxide insulating layer 396 is formed.

  In the case where a silicon oxide layer is formed as the oxide insulating layer 396 and a silicon nitride layer is stacked as the protective insulating layer 398, the silicon oxide layer and the silicon nitride layer are formed using a common silicon target in the same treatment chamber. Can do. First, a sputtering gas containing oxygen is introduced, and a silicon oxide layer is formed using a silicon target mounted in the processing chamber. Next, the sputtering gas is switched to a sputtering gas containing nitrogen and nitriding is performed using the same silicon target. A silicon layer is formed. Since the silicon oxide layer and the silicon nitride layer can be continuously formed without being exposed to the atmosphere, impurities such as hydrogen and moisture can be prevented from being adsorbed on the surface of the silicon oxide layer. In this case, a silicon oxide layer is formed as the oxide insulating layer 396 and a silicon nitride layer is stacked as the protective insulating layer 398, and then hydrogen or moisture contained in the oxide semiconductor layer is diffused into the oxide insulating layer. Heat treatment (temperature: 100 ° C. to 400 ° C.) may be performed.

  After the protective insulating layer is formed, heat treatment may be further performed in the air at 100 ° C. to 200 ° C. for 1 hour to 30 hours. This heat treatment may be performed while maintaining a constant heating temperature, or the temperature is raised from room temperature to a heating temperature of 100 ° C. or more and 200 ° C. or less, and the temperature lowering from the heating temperature to the room temperature is repeated several times. May be. Further, this heat treatment may be performed under reduced pressure before formation of the oxide insulating layer. When the heat treatment is performed under reduced pressure, the heating time can be shortened. Through this heat treatment, a normally-off transistor can be obtained. Therefore, the reliability of the semiconductor device can be improved.

  In addition, when an oxide semiconductor layer serving as a channel formation region is formed over the gate insulating layer, residual moisture in the reaction atmosphere is removed, so that the concentration of hydrogen and hydride in the oxide semiconductor layer is reduced. be able to.

  The above steps can be used for manufacturing a backplane (a substrate on which a transistor is formed) such as a liquid crystal display panel, an electroluminescent display panel, and a display device using electronic ink. Since the above process is performed at a temperature of 400 ° C. or less, the process can be applied to a manufacturing process using a glass substrate having a thickness of 1 mm or less and a side exceeding 1 m. In addition, since all the steps can be performed at a processing temperature of 400 ° C. or less, it is not necessary to consume a great deal of energy for manufacturing the display panel.

  By applying the above transistor to the transistor included in the semiconductor device described in any of Embodiments 1 to 4, discharge of the battery in the standby state can be suppressed. That is, the standby power of the semiconductor device can be reduced. In addition, the life of the semiconductor device can be extended by suppressing battery discharge in the standby state.

  Further, by forming all of the transistors included in the semiconductor device described in any of Embodiments 1 to 4 using the above-described transistors, the manufacturing process can be reduced, yield can be improved, and manufacturing cost can be reduced.

  Note that the content of this embodiment or part of the content can be freely combined with the content of another embodiment or part of the content.

(Embodiment 8)
In this embodiment, an example of a transistor included in the semiconductor device described in any of Embodiments 1 to 4 will be described. Specifically, an example of a transistor in which a channel formation region is formed using an oxide semiconductor will be described.

  One embodiment of a transistor and a manufacturing method thereof in this embodiment will be described with reference to FIGS.

  FIGS. 18A to 18D illustrate an example of a cross-sectional structure of a transistor. A transistor 360 illustrated in FIG. 18D has a bottom-gate structure called a channel protection type (also referred to as a channel stop type) and is also referred to as an inverted staggered transistor.

  Although the transistor 360 is described using a single-gate transistor, a multi-gate transistor including a plurality of channel formation regions can be formed as needed.

  Hereinafter, a process for manufacturing the transistor 360 over the substrate 320 will be described with reference to FIGS.

  First, after a conductive film is formed over the substrate 320 having an insulating surface, a gate electrode layer 361 is formed by a first photolithography process. Note that the resist mask may be formed by an inkjet method. When the resist mask is formed by an ink-jet method, a manufacturing cost can be reduced because a photomask is not used.

  The gate electrode layer 361 is formed of a single layer or stacked layers using a metal material such as molybdenum, titanium, chromium, tantalum, tungsten, aluminum, copper, neodymium, or scandium, or an alloy material containing these as a main component. Can be formed.

  Next, a gate insulating layer 322 is formed over the gate electrode layer 361.

  In this embodiment, a silicon oxynitride layer with a thickness of 100 nm or less is formed as the gate insulating layer 322 by a plasma CVD method.

  Next, an oxide semiconductor film with a thickness of 2 nm to 200 nm is formed over the gate insulating layer 322 and processed into an island-shaped oxide semiconductor layer by a second photolithography step. In this embodiment, the oxide semiconductor film is formed by a sputtering method using an In—Ga—Zn—O-based metal oxide target.

  In this case, it is preferable to form the oxide semiconductor film while removing residual moisture in the treatment chamber. This is for preventing hydrogen, a hydroxyl group, and moisture from being contained in the oxide semiconductor film.

In order to remove moisture remaining in the treatment chamber, an adsorption-type vacuum pump is preferably used. For example, it is preferable to use a cryopump, an ion pump, or a titanium sublimation pump. The exhaust means may be a turbo pump provided with a cold trap. A treatment chamber evacuated using a cryopump is included in an oxide semiconductor film formed in the treatment chamber because, for example, hydrogen atoms, a compound containing hydrogen atoms such as water (H ₂ O), or the like is evacuated. Impurity concentration can be reduced.

  As a sputtering gas used for forming the oxide semiconductor film, a high-purity gas from which impurities such as hydrogen, water, a hydroxyl group, or hydride are removed to about several ppm and several ppb is preferably used.

  Next, dehydration or dehydrogenation of the oxide semiconductor layer is performed. The temperature of the first heat treatment for dehydration or dehydrogenation is 400 ° C to 750 ° C, preferably 400 ° C to less than the strain point of the substrate. Here, a substrate is introduced into an electric furnace which is one of heat treatment apparatuses, and the oxide semiconductor layer is subjected to heat treatment at 450 ° C. for 1 hour in a nitrogen atmosphere, and then the oxide semiconductor layer is exposed to the atmosphere without being exposed to air. The oxide semiconductor layer 332 is obtained by preventing re-mixing of water and hydrogen into the semiconductor layer (see FIG. 18A).

Next, plasma treatment using a gas such as N ₂ O, N ₂ , or Ar is performed. By this plasma treatment, adsorbed water or the like attached to the exposed surface of the oxide semiconductor layer is removed. Further, plasma treatment may be performed using a mixed gas of oxygen and argon.

  Next, after an oxide insulating layer is formed over the gate insulating layer 322 and the oxide semiconductor layer 332, a resist mask is formed by a third photolithography step, and selective etching is performed, so that the oxide insulating layer 366 is formed. After forming, the resist mask is removed.

  In this embodiment, a 200-nm-thick silicon oxide film is formed as the oxide insulating layer 366 by a sputtering method. The substrate temperature at the time of film formation may be from room temperature to 300 ° C., and is 100 ° C. in this embodiment. The silicon oxide film can be formed by a sputtering method in a rare gas (typically argon) atmosphere, an oxygen atmosphere, or a rare gas (typically argon) and oxygen atmosphere. Further, a silicon oxide target or a silicon target can be used as the target. For example, silicon oxide can be formed by a sputtering method in an oxygen and nitrogen atmosphere using a silicon target.

  In this case, the oxide insulating layer 366 is preferably formed while moisture remaining in the treatment chamber is removed. This is for preventing hydrogen, a hydroxyl group, and moisture from being contained in the oxide semiconductor layer 332 and the oxide insulating layer 366.

In order to remove moisture remaining in the treatment chamber, an adsorption-type vacuum pump is preferably used. For example, it is preferable to use a cryopump, an ion pump, or a titanium sublimation pump. The exhaust means may be a turbo pump provided with a cold trap. A treatment chamber evacuated using a cryopump is included in the oxide insulating layer 366 formed in the treatment chamber because a hydrogen atom, a compound containing hydrogen atoms such as water (H ₂ O), or the like is exhausted, for example. The concentration of impurities to be reduced can be reduced.

  As a sputtering gas used for forming the oxide insulating layer 366, a high-purity gas from which impurities such as hydrogen, water, a hydroxyl group, or hydride are removed to about several ppm and several ppb is preferably used.

  Next, second heat treatment (preferably 200 to 400 ° C., for example, 250 to 350 ° C.) may be performed in an inert gas atmosphere or an oxygen gas atmosphere. For example, the second heat treatment is performed at 250 ° C. for 1 hour in a nitrogen atmosphere. When the second heat treatment is performed, part of the oxide semiconductor layer (a channel formation region) is heated in contact with the oxide insulating layer 366.

  In this embodiment, the oxide semiconductor layer 332 which is further provided with the oxide insulating layer 366 and is partially exposed is subjected to heat treatment in an atmosphere of nitrogen or an inert gas, or under reduced pressure. The exposed region of the oxide semiconductor layer 332 that is not covered with the oxide insulating layer 366 can be reduced in resistance by heat treatment in an atmosphere of nitrogen, an inert gas, or reduced pressure. For example, heat treatment is performed at 250 ° C. for 1 hour in a nitrogen atmosphere.

  By the heat treatment in a nitrogen atmosphere with respect to the oxide semiconductor layer 332 provided with the oxide insulating layer 366, the exposed region of the oxide semiconductor layer 332 has a low resistance, and a region having a different resistance (a hatched region in FIG. 18B) And an oxide semiconductor layer 362 having a white background).

  Next, after a conductive film is formed over the gate insulating layer 322, the oxide semiconductor layer 362, and the oxide insulating layer 366, a resist mask is formed by a fourth photolithography step, and etching is performed selectively. After the electrode layer 365a and the drain electrode layer 365b are formed, the resist mask is removed (see FIG. 18C).

  As a material of the source electrode layer 365a and the drain electrode layer 365b, an element selected from Al, Cr, Cu, Ta, Ti, Mo, and W, an alloy containing the above-described element as a component, or a combination of the above-described elements Alloy films and the like. The metal conductive film may have a single layer structure or a stacked structure of two or more layers.

  Through the above steps, the oxide semiconductor film after film formation is subjected to heat treatment for dehydration or dehydrogenation to reduce resistance, and then part of the oxide semiconductor film is selectively formed. Make oxygen excess. As a result, the channel formation region 363 that overlaps with the gate electrode layer 361 is i-type, and a high-resistance source region 364a that overlaps the source electrode layer 365a and a high-resistance drain region 364b that overlaps the drain electrode layer 365b are formed in a self-aligned manner. Is done. Through the above process, the transistor 360 is formed.

  Further, heat treatment may be performed at 100 ° C. to 200 ° C. for 1 hour to 30 hours in the air. In this embodiment, heat treatment is performed at 150 ° C. for 10 hours. This heat treatment may be performed while maintaining a constant heating temperature, or the temperature is raised from room temperature to a heating temperature of 100 ° C. or more and 200 ° C. or less, and the temperature lowering from the heating temperature to the room temperature is repeated several times. May be. Further, this heat treatment may be performed under reduced pressure before formation of the oxide insulating film. When the heat treatment is performed under reduced pressure, the heating time can be shortened. Through this heat treatment, a transistor in which hydrogen is taken into the oxide insulating layer from the oxide semiconductor layer and is normally off can be obtained. Therefore, the reliability of the semiconductor device can be improved.

  Note that by forming the high-resistance drain region 364b (and the high-resistance source region 364a) in the oxide semiconductor layer overlapping with the drain electrode layer 365b (and the source electrode layer 365a), the reliability of the transistor can be improved. it can. Specifically, by forming the high resistance drain region 364b, a structure in which the conductivity can be changed stepwise from the drain electrode layer to the high resistance drain region 364b and the channel formation region 363 can be obtained. Therefore, when the drain electrode layer 365b is connected to a wiring that supplies the high power supply potential VDD, the high resistance drain region becomes a buffer even when a high voltage is applied between the gate electrode layer 361 and the drain electrode layer 365b. Local concentration of electrolysis is unlikely to occur, and a structure in which the breakdown voltage of the transistor is improved can be obtained.

  A protective insulating layer 323 is formed over the source electrode layer 365a, the drain electrode layer 365b, and the oxide insulating layer 366. In this embodiment, the protective insulating layer 323 is formed using a silicon nitride film (see FIG. 18D).

  Note that an oxide insulating layer may be further formed over the source electrode layer 365a, the drain electrode layer 365b, and the oxide insulating layer 366, and the protective insulating layer 323 may be stacked over the oxide insulating layer.

  By applying the above transistor to the transistor included in the semiconductor device described in any of Embodiments 1 to 4, discharge of the battery in the standby state can be suppressed. That is, the standby power of the semiconductor device can be reduced. In addition, the life of the semiconductor device can be extended by suppressing battery discharge in the standby state.

  Further, by forming all of the transistors included in the semiconductor device described in any of Embodiments 1 to 4 using the above-described transistors, the manufacturing process can be reduced, yield can be improved, and manufacturing cost can be reduced.

  Note that the content of this embodiment or part of the content can be freely combined with the content of another embodiment or part of the content.

(Embodiment 9)
In this embodiment, usage examples of the semiconductor device described in any of Embodiments 1 to 4 will be described with reference to FIGS.

  As shown in FIG. 19, the semiconductor device has a wide range of uses. For example, banknotes, coins, securities, bearer bonds, certificate documents (driver's license, resident's card, etc., see FIG. 19A), record Medium (DVD software, video tape, etc., see FIG. 19 (B)), packaging containers (wrapping paper, bottles, etc., see FIG. 19 (C)), vehicles (bicycles, etc., see FIG. 19 (D)), Items such as personal items (such as bags and glasses), foods, plants, animals, human bodies, clothing, daily necessities, or electronic devices (liquid crystal display devices, EL display devices, television receivers, or mobile phones) Alternatively, it can be used in a tag attached to each article (see FIGS. 19E and 19F).

  The semiconductor device 1500 is fixed to an article by being mounted on a printed board, pasted on a surface, or embedded. For example, if it is a book, it is embedded in paper, or if it is a package made of an organic resin, it is embedded in the organic resin and fixed to each article. Since the semiconductor device 1500 is small, thin, and lightweight, the design of the article itself is not impaired even after the semiconductor apparatus 1500 is fixed to the article. In addition, an authentication function can be provided by providing the semiconductor device 1500 in bills, coins, securities, bearer bonds, certificates, etc., and forgery can be prevented by using this authentication function. . In addition, by attaching the semiconductor device of the present invention to packaging containers, recording media, personal items, foods, clothing, daily necessities, electronic devices, etc., it is possible to improve the efficiency of systems such as inspection systems. . Further, even for vehicles, by attaching the semiconductor device 1500, security against theft can be improved.

  As described above, since the semiconductor device described in any of the above embodiments can be used for each application described in this embodiment, data used for information exchange can be maintained as an accurate value. Authenticity or security can be improved.

  Note that the content of this embodiment or part of the content can be freely combined with the content of another embodiment or part of the content.

DESCRIPTION OF SYMBOLS 10 Antenna 11 Battery 12 Demodulation circuit 13 Signal processing part 14 Power control circuit 15 Transistor 20 Antenna 21 Battery 22 Timer 23 Signal processing part 24 Power control circuit 25 Transistor 30 Antenna 31 Secondary battery 32 Rectification circuit 33 Charging circuit 34 Stabilization power supply circuit 35 demodulation circuit 36 signal processing unit 37 power control circuit 38 transistor 40 antenna 41 secondary battery 42 rectifier circuit 43 charging circuit 44 stabilizing power supply circuit 45 demodulation circuit 46 signal processing unit 47 power control circuit 48 logic circuit 49 clock generation circuit 50 sensor 51 memory circuit 52 modulation circuit 80 P-type transistor 81 N-type transistor 82 N-type transistor 83 P-type transistor 84 P-type transistor 85 N-type transistor 86 N-type transistor 87 N-type transistor 88 P-type transistor Jistor 89 P-type transistor 90 N-type transistor 91 N-type transistor 92 N-type transistor 100 Substrate 102 Protective layer 104 Semiconductor region 106 Element isolation insulating layer 108a Gate insulating layer 108b Insulating layer 110a Gate electrode layer 110b Electrode layer 112 Insulating layer 114a Impurity region 114b Impurity region 116 Channel formation region 118 Side wall insulating layer 120a High concentration impurity region 120b High concentration impurity region 122 Metal layer 124a Metal compound region 124b Metal compound region 126 Interlayer insulation layer 128 Interlayer insulation layer 130a Source electrode layer 130b Drain electrode layer 130c Electrode layer 132 Insulating layer 134 Conductive layer 136a Electrode layer 136b Electrode layer 136c Electrode layer 136d Gate electrode layer 138 Gate insulating layer 140 Oxide semiconductor layer 142a Source electrode 142b Drain electrode layer 144 Protective insulating layer 146 Interlayer insulating layer 148 Conductive layer 150a Electrode layer 150b Electrode layer 150c Electrode layer 150d Electrode layer 150e Electrode layer 152 Insulating layer 154a Electrode layer 154b Electrode layer 154c Electrode layer 154d Electrode layer 160 P-type transistor 164 N-type transistor 320 Substrate 322 Gate insulating layer 323 Protective insulating layer 332 Oxide semiconductor layer 360 Transistor 361 Gate electrode layer 362 Oxide semiconductor layer 363 Channel formation region 364a Source region 364b Drain region 365a Source electrode layer 365b Drain electrode layer 366 Oxide Insulating layer 390 Transistor 391 Gate electrode layer 392 Oxide semiconductor layer 393 Oxide semiconductor film 394 Substrate 395a Source electrode layer 395b Drain electrode layer 396 Oxide insulating layer 397 Gate insulating layer 398 Protective insulating layer 399 Oxide semiconductor layer 423 Opening 450 Substrate 452 Gate insulating layer 457 Insulating layer 460 Transistor 461 Gate electrode layer 461a Gate electrode layer 461b Gate electrode layer 462 Oxide semiconductor layer 464 Wiring layer 465a Source electrode layer or Drain electrode layer 465a1 Source electrode layer or drain electrode layer 465a2 Source electrode layer or drain electrode layer 465b Source electrode layer or drain electrode layer 468 Wiring layer 1500 Semiconductor device

Claims (6)

An antenna,
Battery,
A demodulation circuit for demodulating a signal input from the antenna;
A signal processing unit that operates using a signal input from the demodulation circuit and a power supply voltage supplied from the battery;
A power control circuit controlled by a signal input from the demodulation circuit,
The signal processing unit
A transistor whose switching is controlled by a signal input from the power control circuit;
And a functional circuit electrically connected to the anode or cathode of the battery through the transistor,
The channel formation region of the transistor is a semiconductor device including an oxide semiconductor having a hydrogen concentration of 5 × 10 ¹⁹ (atoms / cm ³ ) or less. An antenna,
Battery,
A timer that periodically outputs a signal;
A signal processing unit that operates using a signal input from the timer and a power supply voltage supplied from the battery;
A power control circuit controlled by a signal input from the timer,
The signal processing unit
A transistor whose switching is controlled by a signal input from the power control circuit;
And a functional circuit electrically connected to the anode or cathode of the battery through the transistor,
The channel formation region of the transistor is a semiconductor device including an oxide semiconductor having a hydrogen concentration of 5 × 10 ¹⁹ (atoms / cm ³ ) or less. In claim 1 or claim 2,
The battery is a secondary battery;
A rectifier circuit for rectifying a signal input from the antenna;
A charging circuit that charges the secondary battery using a signal input from the rectifier circuit;
A stabilized power supply circuit that generates the power supply voltage using the secondary battery. In any one of Claims 1 thru | or 3,
The signal processing unit has a logic gate;
A semiconductor device in which electrical connection between the logic gate and the cathode of the battery is controlled by the transistor. In claim 4,
The logic gate comprises an N-type transistor;
A semiconductor device in which a channel formation region of the N-type transistor is formed of the oxide semiconductor. In claim 4,
The logic gate is composed of a P-type transistor and an N-type transistor;
The channel formation region of the P-type transistor is composed of a semiconductor whose main constituent element is silicon,
The channel formation region of the N-type transistor is a semiconductor device composed of a semiconductor containing silicon as a main constituent element or the oxide semiconductor.

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